diff --git a/router/dataplane.go b/router/dataplane.go
index 4ffcef279..d7e84f3cf 100644
--- a/router/dataplane.go
+++ b/router/dataplane.go
@@ -137,9 +137,8 @@ type BatchConn interface {
 	// @ ensures  io.token(old(MultiReadBioNext(place, prophecyM)))
 	// @ ensures  old(MultiReadBioCorrectIfs(place, prophecyM, ifsToIO_ifs(ingressID)))
 	// @ ensures  err == nil ==>
-	// @	forall i int :: { &msgs[i] } 0 <= i && i < n ==>
-	// @	unfolding acc(msgs[i].Mem(), R56) in absIO_val(dp, msgs[i].Buffers[0], ingressID) ==
-	// @    old(MultiReadBioIO_val(place, n)[i])
+	// @ 	forall i int :: { &msgs[i] } 0 <= i && i < n ==>
+	// @ 		MsgToAbsVal(dp, &msgs[i], ingressID) == old(MultiReadBioIO_val(place, n)[i])
 	// TODO (Markus): uint16 or option[io.IO_ifs] for ingress
 	ReadBatch(msgs underlayconn.Messages /*@, ghost ingressID uint16, ghost prophecyM int, ghost place io.Place, ghost dp io.DataPlaneSpec @*/) (n int, err error)
 	// @ requires  acc(addr.Mem(), _)
@@ -152,10 +151,19 @@ type BatchConn interface {
 	// (VerifiedSCION) opted for less reusable spec for WriteBatch for
 	// performance reasons.
 	// @ requires  len(msgs) == 1
-	// @ preserves acc(msgs[0].Mem(), R50) && msgs[0].HasActiveAddr()
+	// @ requires  acc(msgs[0].Mem(), R50) && msgs[0].HasActiveAddr()
+	// @ ensures   acc(msgs[0].Mem(), R50) && msgs[0].HasActiveAddr()
 	// @ ensures   err == nil ==> 0 <= n && n <= len(msgs)
 	// @ ensures   err != nil ==> err.ErrorMem()
-	WriteBatch(msgs underlayconn.Messages, flags int) (n int, err error)
+	// contracts for IO-spec
+	// @ requires  dp.Valid()
+	// @ requires  MsgToAbsVal(dp, &msgs[0], egressID) == ioAbsPkts
+	// @ requires  io.token(place) && io.CBioIO_bio3s_send(place, ioAbsPkts)
+	// @ ensures   dp.Valid()
+	// (VerifiedSCION) the permission to the protocol must always be returned, otherwise the router could not continue
+	// after failing to send a packet.
+	// @ ensures   io.token(old(io.dp3s_iospec_bio3s_send_T(place, ioAbsPkts)))
+	WriteBatch(msgs underlayconn.Messages, flags int /*@, ghost egressID uint16, ghost place io.Place, ghost ioAbsPkts io.IO_val, ghost dp io.DataPlaneSpec @*/) (n int, err error)
 	// @ requires Mem()
 	// @ ensures  err != nil ==> err.ErrorMem()
 	// @ decreases
@@ -732,6 +740,7 @@ func (d *DataPlane) AddNextHopBFD(ifID uint16, src, dst *net.UDPAddr, cfg contro
 // @ requires dp.Valid()
 // @ requires d.DpAgreesWithSpec(dp)
 // @ requires io.token(place) && dp.dp3s_iospec_ordered(state, place)
+// @ #backend[moreJoins()]
 func (d *DataPlane) Run(ctx context.Context /*@, ghost place io.Place, ghost state io.IO_dp3s_state_local, ghost dp io.DataPlaneSpec @*/) error {
 	// @ share d, ctx
 	d.mtx.Lock()
@@ -791,8 +800,8 @@ func (d *DataPlane) Run(ctx context.Context /*@, ghost place io.Place, ghost sta
 		// @ requires let d := *dPtr in
 		// @ 	d.DpAgreesWithSpec(dp)
 		// @ requires acc(ioLock.LockP(), _) && ioLock.LockInv() == SharedInv!< dp, ioSharedArg !>;
+		// @ #backend[moreJoins()]
 		func /*@ rc @*/ (ingressID uint16, rd BatchConn, dPtr **DataPlane /*@, ghost ioLock *sync.Mutex, ghost ioSharedArg SharedArg, ghost dp io.DataPlaneSpec @*/) {
-			// @ ghost ioIngressID := ifsToIO_ifs(ingressID)
 			d := *dPtr
 			msgs := conn.NewReadMessages(inputBatchCnt)
 			// @ requires forall i int :: { &msgs[i] } 0 <= i && i < len(msgs) ==>
@@ -855,8 +864,11 @@ func (d *DataPlane) Run(ctx context.Context /*@, ghost place io.Place, ghost sta
 			// @ invariant ingressID in d.getDomForwardingMetrics()
 			// @ invariant acc(rd.Mem(), _)
 			// @ invariant processor.sInit() && processor.sInitD() === d
+			// @ invariant processor.getIngressID() == ingressID
 			// @ invariant acc(ioLock.LockP(), _) && ioLock.LockInv() == SharedInv!< dp, ioSharedArg !>
+			// @ invariant d.DpAgreesWithSpec(dp) && dp.Valid()
 			for d.running {
+				// @ ghost ioIngressID := ifsToIO_ifs(ingressID)
 				// Multi recv event
 				// @ ghost ioLock.Lock()
 				// @ unfold SharedInv!< dp, ioSharedArg !>()
@@ -864,14 +876,24 @@ func (d *DataPlane) Run(ctx context.Context /*@, ghost place io.Place, ghost sta
 				// @ ghost numberOfReceivedPacketsProphecy := AllocProphecy()
 				// @ ExtractMultiReadBio(dp, t, numberOfReceivedPacketsProphecy, s)
 				// @ MultiUpdateElemWitness(t, numberOfReceivedPacketsProphecy, ioIngressID, s, ioSharedArg)
-				// @ ghost ioValSeq := MultiReadBioIO_val(t,numberOfReceivedPacketsProphecy)
+				// @ ghost ioValSeq := MultiReadBioIO_val(t, numberOfReceivedPacketsProphecy)
 
 				// @ ghost sN := MultiReadBioUpd(t, numberOfReceivedPacketsProphecy, s)
 				// @ ghost tN := MultiReadBioNext(t, numberOfReceivedPacketsProphecy)
 				// @ assert dp.dp3s_iospec_ordered(sN, tN)
+				// @ BeforeReadBatch:
 				pkts, err := rd.ReadBatch(msgs /*@, ingressID, numberOfReceivedPacketsProphecy, t , dp @*/)
+				// @ assert old[BeforeReadBatch](MultiReadBioIO_val(t, numberOfReceivedPacketsProphecy)) == ioValSeq
+				// @ assert err == nil ==>
+				// @ 	forall i int :: { &msgs[i] } 0 <= i && i < pkts ==>
+				// @ 		ioValSeq[i] == old[BeforeReadBatch](MultiReadBioIO_val(t, numberOfReceivedPacketsProphecy)[i])
+				// @ assert err == nil ==>
+				// @ 	forall i int :: { &msgs[i] } 0 <= i && i < pkts ==> MsgToAbsVal(dp, &msgs[i], ingressID) == ioValSeq[i]
 				// @ ghost *ioSharedArg.State = sN
 				// @ ghost *ioSharedArg.Place = tN
+				// @ assert err == nil ==>
+				// @ 	forall i int :: { &msgs[i] } 0 <= i && i < pkts ==>
+				// @ 		MsgToAbsVal(dp, &msgs[i], ingressID) == old[BeforeReadBatch](MultiReadBioIO_val(t, numberOfReceivedPacketsProphecy)[i])
 				// @ MultiElemWitnessConv(ioSharedArg.IBufY, ioIngressID, ioValSeq)
 				// @ fold SharedInv!< dp, ioSharedArg !>()
 				// @ ioLock.Unlock()
@@ -893,6 +915,8 @@ func (d *DataPlane) Run(ctx context.Context /*@, ghost place io.Place, ghost sta
 				// @ 	!msgs[i].HasWildcardPermAddr()
 				// @ assert forall i int :: { &msgs[i] } 0 <= i && i < pkts ==>
 				// @ 	msgs[i].GetN() <= len(msgs[i].GetFstBuffer())
+				// @ assert forall i int :: { &msgs[i] } 0 <= i && i < pkts ==>
+				// @ 	MsgToAbsVal(dp, &msgs[i], ingressID) == ioValSeq[i]
 
 				// (VerifiedSCION) using regular for loop instead of range loop to avoid unnecessary
 				// complications with permissions
@@ -915,6 +939,15 @@ func (d *DataPlane) Run(ctx context.Context /*@, ghost place io.Place, ghost sta
 				// @ invariant forall i int :: { &msgs[i] } 0 <= i && i < pkts ==>
 				// @ 	msgs[i].GetN() <= len(msgs[i].GetFstBuffer())
 				// @ invariant processor.sInit() && processor.sInitD() === d
+				// @ invariant processor.getIngressID() == ingressID
+				// contracts for IO-spec
+				// @ invariant pkts <= len(ioValSeq)
+				// @ invariant d.DpAgreesWithSpec(dp) && dp.Valid()
+				// @ invariant ioIngressID == ifsToIO_ifs(ingressID)
+				// @ invariant acc(ioLock.LockP(), _) && ioLock.LockInv() == SharedInv!< dp, ioSharedArg !>;
+				// @ invariant forall i int :: { &msgs[i] } i0 <= i && i < pkts ==>
+				// @ 	MsgToAbsVal(dp, &msgs[i], ingressID) == ioValSeq[i]
+				// @ invariant MultiElemWitnessWithIndex(ioSharedArg.IBufY, ioIngressID, ioValSeq, i0)
 				for i0 := 0; i0 < pkts; i0++ {
 					// @ assert &msgs[:pkts][i0] == &msgs[i0]
 					// @ preserves 0 <= i0 && i0 < pkts && pkts <= len(msgs)
@@ -946,12 +979,24 @@ func (d *DataPlane) Run(ctx context.Context /*@, ghost place io.Place, ghost sta
 					// @ assert p.Buffers === m.Buffers
 					// @ assert acc(&p.Buffers[0])
 					// @ assert p.N <= len(p.Buffers[0])
-					// @ sl.SplitRange_Bytes(p.Buffers[0], 0, p.N, writePerm)
+					// @ sl.SplitRange_Bytes(p.Buffers[0], 0, p.N, HalfPerm)
 					tmpBuf := p.Buffers[0][:p.N]
+					// @ ghost absPktTmpBuf := absIO_val(dp, tmpBuf, ingressID)
+					// @ ghost absPktBuf0   := absIO_val(dp, msgs[i0].Buffers[0], ingressID)
+					// @ assert msgs[i0] === p
+					// @ absIO_valWidenLemma(dp, p.Buffers[0], ingressID, p.N)
+					// @ assert absPktTmpBuf.isIO_val_Pkt2 ==> absPktTmpBuf === absPktBuf0
+					// @ MultiElemWitnessStep(ioSharedArg.IBufY, ioIngressID, ioValSeq, i0)
+					// @ assert ioValSeq[i0].isIO_val_Pkt2 ==>
+					// @ 	ElemWitness(ioSharedArg.IBufY, ioIngressID, ioValSeq[i0].IO_val_Pkt2_2)
+					// @ assert absPktTmpBuf.isIO_val_Pkt2 ==> absPktTmpBuf == ioValSeq[i0]
+					// @ assert ifsToIO_ifs(processor.getIngressID()) == ioIngressID
+					// @ sl.SplitRange_Bytes(p.Buffers[0], 0, p.N, HalfPerm)
 					// @ assert sl.AbsSlice_Bytes(tmpBuf, 0, p.N)
 					// @ assert sl.AbsSlice_Bytes(tmpBuf, 0, len(tmpBuf))
-					result, err /*@ , addrAliasesPkt, newAbsPkt @*/ := processor.processPkt(tmpBuf, srcAddr /*@, ioLock, ioSharedArg, dp@*/)
+					result, err /*@ , addrAliasesPkt, newAbsPkt @*/ := processor.processPkt(tmpBuf, srcAddr /*@, ioLock, ioSharedArg, dp @*/)
 					// @ fold scmpErr.Mem()
+
 					switch {
 					case err == nil:
 						// @ unfold scmpErr.Mem()
@@ -999,6 +1044,13 @@ func (d *DataPlane) Run(ctx context.Context /*@, ghost place io.Place, ghost sta
 						continue
 					}
 
+					// (VerifiedSCION) we currently have this assumption because we cannot think of a sound way to capture
+					// the behaviour of errors.As(...) in our specifications. Nonetheless, we checked extensively that, when
+					// processPkt does not return an error or returns an scmpError (and thus errors.As(err, &scmpErr) succeeds),
+					// result.OutPkt is always non-nil. For the other kinds of errors, the result is nil, but that branch is killed
+					// before this point.
+					// @ assume result.OutPkt != nil
+
 					// Write to OutConn; drop the packet if this would block.
 					// Use WriteBatch because it's the only available function that
 					// supports MSG_DONTWAIT.
@@ -1012,8 +1064,26 @@ func (d *DataPlane) Run(ctx context.Context /*@, ghost place io.Place, ghost sta
 						writeMsgs[0].Addr = result.OutAddr
 					}
 					// @ sl.NilAcc_Bytes()
+					// @ assert absIO_val(dp, result.OutPkt, result.EgressID) == absIO_val(dp, writeMsgs[0].Buffers[0], result.EgressID)
+					// @ assert result.OutPkt != nil ==> newAbsPkt == absIO_val(dp, writeMsgs[0].Buffers[0], result.EgressID)
 					// @ fold acc(writeMsgs[0].Mem(), R50)
-					_, err = result.OutConn.WriteBatch(writeMsgs, syscall.MSG_DONTWAIT)
+
+					// @ ghost ioLock.Lock()
+					// @ unfold SharedInv!< dp, ioSharedArg !>()
+					// @ ghost t, s := *ioSharedArg.Place, *ioSharedArg.State
+					// @ ghost if(newAbsPkt.isIO_val_Pkt2) {
+					// @ 	ApplyElemWitness(s.obuf, ioSharedArg.OBufY, newAbsPkt.IO_val_Pkt2_1, newAbsPkt.IO_val_Pkt2_2)
+					// @ 	assert newAbsPkt.IO_val_Pkt2_2 in AsSet(s.obuf[newAbsPkt.IO_val_Pkt2_1])
+					// @ 	assert dp.dp3s_iospec_bio3s_send_guard(s, t, newAbsPkt)
+					// @ } else { assert newAbsPkt.isIO_val_Unsupported }
+					// @ unfold dp.dp3s_iospec_ordered(s, t)
+					// @ unfold dp.dp3s_iospec_bio3s_send(s, t)
+					// @ io.TriggerBodyIoSend(newAbsPkt)
+					// @ ghost tN := io.dp3s_iospec_bio3s_send_T(t, newAbsPkt)
+					_, err = result.OutConn.WriteBatch(writeMsgs, syscall.MSG_DONTWAIT /*@, result.EgressID, t, newAbsPkt, dp @*/)
+					// @ ghost *ioSharedArg.Place = tN
+					// @ fold SharedInv!< dp, ioSharedArg !>()
+					// @ ghost ioLock.Unlock()
 					// @ unfold acc(writeMsgs[0].Mem(), R50)
 					// @ ghost if addrAliasesPkt && result.OutAddr != nil {
 					// @	apply acc(result.OutAddr.Mem(), R15) --* acc(sl.AbsSlice_Bytes(tmpBuf, 0, len(tmpBuf)), R15)
@@ -1280,7 +1350,7 @@ type processResult struct {
 }
 
 // @ requires acc(d.Mem(), _) && d.getMacFactory() != nil
-// @ ensures  res.sInit() && res.sInitD() == d
+// @ ensures  res.sInit() && res.sInitD() == d && res.getIngressID() == ingressID
 // @ decreases
 func newPacketProcessor(d *DataPlane, ingressID uint16) (res *scionPacketProcessor) {
 	var verScionTmp gopacket.SerializeBuffer
@@ -1309,6 +1379,7 @@ func newPacketProcessor(d *DataPlane, ingressID uint16) (res *scionPacketProcess
 
 // @ preserves p.sInit()
 // @ ensures   p.sInitD()         == old(p.sInitD())
+// @ ensures   p.getIngressID()   == old(p.getIngressID())
 // @ ensures   p.sInitRawPkt()    == nil
 // @ ensures   p.sInitPath()      == nil
 // @ ensures   p.sInitHopField()  == path.HopField{}
@@ -1341,10 +1412,11 @@ func (p *scionPacketProcessor) reset() (err error) {
 // @ 	d.WellConfigured()        &&
 // @ 	d.getValSvc() != nil      &&
 // @ 	d.getValForwardingMetrics() != nil &&
-// @	d.DpAgreesWithSpec(dp)
+// @ 	d.DpAgreesWithSpec(dp)
 // @ ensures  p.sInit()
 // @ ensures  acc(p.sInitD().Mem(), _)
 // @ ensures  p.sInitD() == old(p.sInitD())
+// @ ensures  p.getIngressID() == old(p.getIngressID())
 // @ ensures  p.sInitD().validResult(respr, addrAliasesPkt)
 // @ ensures  acc(sl.AbsSlice_Bytes(rawPkt, 0, len(rawPkt)), 1 - R15)
 // @ ensures  addrAliasesPkt ==> (
@@ -1358,13 +1430,15 @@ func (p *scionPacketProcessor) reset() (err error) {
 // @ requires dp.Valid()
 // @ requires acc(ioLock.LockP(), _) && ioLock.LockInv() == SharedInv!< dp, ioSharedArg !>;
 // @ requires let absPkt := absIO_val(dp, rawPkt, p.getIngressID()) in
-// @	absPkt.isIO_val_Pkt2 ==> ElemWitness(ioSharedArg.IBufY, ifsToIO_ifs(p.getIngressID()), absPkt.IO_val_Pkt2_2)
-// @ ensures reserr == nil && newAbsPkt.isIO_val_Pkt2 ==>
-// @	ElemWitness(ioSharedArg.OBufY, newAbsPkt.IO_val_Pkt2_1, newAbsPkt.IO_val_Pkt2_2)
-// @ ensures reserr == nil && newAbsPkt.isIO_val_Pkt2 ==> respr.OutPkt != nil &&
-// @	newAbsPkt == absIO_val(dp, respr.OutPkt, respr.EgressID)
-// TODO: On a first step, we will prove that whenever we have a valid scion packet in processSCION,
-// the correct "next packet" is computed
+// @ 	absPkt.isIO_val_Pkt2 ==> ElemWitness(ioSharedArg.IBufY, ifsToIO_ifs(p.getIngressID()), absPkt.IO_val_Pkt2_2)
+// @ ensures dp.Valid()
+// @ ensures respr.OutPkt != nil ==>
+// @ 	newAbsPkt == absIO_val(dp, respr.OutPkt, respr.EgressID)
+// @ ensures (respr.OutPkt == nil) == (newAbsPkt == io.IO_val_Unit{})
+// @ ensures newAbsPkt.isIO_val_Pkt2 ==>
+// @ 	ElemWitness(ioSharedArg.OBufY, newAbsPkt.IO_val_Pkt2_1, newAbsPkt.IO_val_Pkt2_2)
+// @ ensures reserr != nil && respr.OutPkt != nil ==> newAbsPkt.isIO_val_Unsupported
+// @ ensures respr.OutPkt != nil ==> newAbsPkt == absIO_val(dp, respr.OutPkt, respr.EgressID)
 func (p *scionPacketProcessor) processPkt(rawPkt []byte,
 	srcAddr *net.UDPAddr /*@, ghost ioLock *sync.Mutex, ghost ioSharedArg SharedArg, ghost dp io.DataPlaneSpec @*/) (respr processResult, reserr error /*@ , addrAliasesPkt bool, ghost newAbsPkt io.IO_val  @*/) {
 
@@ -1650,8 +1724,10 @@ func (p *scionPacketProcessor) processIntraBFD(data []byte) (res error) {
 // @	absPkt.isIO_val_Pkt2 ==> ElemWitness(ioSharedArg.IBufY, ifsToIO_ifs(p.ingressID), absPkt.IO_val_Pkt2_2)
 // @ ensures reserr == nil && newAbsPkt.isIO_val_Pkt2 ==>
 // @	ElemWitness(ioSharedArg.OBufY, newAbsPkt.IO_val_Pkt2_1, newAbsPkt.IO_val_Pkt2_2)
-// @ ensures reserr == nil && newAbsPkt.isIO_val_Pkt2 ==> respr.OutPkt != nil &&
+// @ ensures respr.OutPkt != nil ==>
 // @	newAbsPkt == absIO_val(dp, respr.OutPkt, respr.EgressID)
+// @ ensures reserr != nil && respr.OutPkt != nil ==>
+// @ 	newAbsPkt.isIO_val_Unsupported
 func (p *scionPacketProcessor) processSCION( /*@ ghost ub []byte, ghost llIsNil bool, ghost startLL int, ghost endLL int, ghost ioLock *sync.Mutex, ghost ioSharedArg SharedArg, ghost dp io.DataPlaneSpec @*/ ) (respr processResult, reserr error /*@ , addrAliasesPkt bool, ghost newAbsPkt io.IO_val  @*/) {
 
 	var ok bool
@@ -2819,7 +2895,6 @@ func (p *scionPacketProcessor) process( /*@ ghost ub []byte, ghost llIsNil bool,
 		}
 		// verify the new block
 		if r, err := p.verifyCurrentMAC(); err != nil {
-			//  fold acc(p.scionLayer.Mem(ub), R3)
 			// @ p.scionLayer.DowngradePerm(ub)
 			return r, serrors.WithCtx(err, "info", "after xover") /*@, false, io.IO_val_Unit{} @*/
 		}
diff --git a/router/dataplane_concurrency_model.gobra b/router/dataplane_concurrency_model.gobra
index 10dfc049d..79e273864 100644
--- a/router/dataplane_concurrency_model.gobra
+++ b/router/dataplane_concurrency_model.gobra
@@ -99,6 +99,7 @@ pure func MultiReadBioCorrectIfs(
 }
 
 ghost
+opaque
 requires 0 <= expectedPkts && MultiReadBio(t, expectedPkts)
 ensures len(res) == expectedPkts
 decreases expectedPkts
@@ -159,8 +160,10 @@ requires ElemAuth(s.ibuf, y.IBufY) && ElemAuth(s.obuf, y.OBufY)
 ensures  MultiReadBio(t, n)
 ensures  MultiReadBioUpd(t, n, s) == old(MultiReadBioUpd(t, n, s))
 ensures  MultiReadBioNext(t, n) == old(MultiReadBioNext(t, n))
-ensures  ElemAuth(MultiReadBioUpd(t, n, s).ibuf, y.IBufY) && ElemAuth(MultiReadBioUpd(t, n, s).obuf, y.OBufY)
-ensures  0 <= n && MultiReadBioCorrectIfs(t, n, k) ==> MultiElemWitness(y.IBufY, k, MultiReadBioIO_val(t, n))
+ensures  ElemAuth(MultiReadBioUpd(t, n, s).ibuf, y.IBufY) 
+ensures  ElemAuth(MultiReadBioUpd(t, n, s).obuf, y.OBufY)
+ensures  0 <= n && MultiReadBioCorrectIfs(t, n, k) ==>
+	MultiElemWitness(y.IBufY, k, MultiReadBioIO_val(t, n))
 decreases n
 func MultiUpdateElemWitness(
 	t io.Place,
@@ -180,6 +183,7 @@ func MultiUpdateElemWitness(
 	}
 
 	if 0 <= n && MultiReadBioCorrectIfs(t, n, k) {
+		reveal MultiReadBioIO_val(t, n)
 		fold MultiElemWitness(y.IBufY, k, MultiReadBioIO_val(t, n))
 	}
 }
@@ -215,6 +219,16 @@ func MultiElemWitnessConv(y ElemRA,k Key, es seq[io.IO_val]) {
 	multiElemWitnessConvAux(y,k,es,0)
 }
 
+ghost
+requires 0 <= currIdx && currIdx < len(es)
+requires MultiElemWitnessWithIndex(y, k, es, currIdx)
+ensures  es[currIdx].isIO_val_Pkt2 ==> ElemWitness(y, k, es[currIdx].IO_val_Pkt2_2)
+ensures  MultiElemWitnessWithIndex(y, k, es, currIdx + 1)
+decreases
+func MultiElemWitnessStep(y ElemRA, k Key, es seq[io.IO_val], currIdx int) {
+	unfold MultiElemWitnessWithIndex(y, k, es, currIdx)
+}
+
 ghost
 requires i >= 0
 requires MultiElemWitness(y,k,es[i:])
diff --git a/router/io-spec.gobra b/router/io-spec.gobra
index 763b5a43d..a67c38e58 100644
--- a/router/io-spec.gobra
+++ b/router/io-spec.gobra
@@ -17,12 +17,14 @@
 package router
 
 import (
-	sl "verification/utils/slices"
-	"verification/io"
-	"verification/dependencies/encoding/binary"
 	"github.com/scionproto/scion/pkg/slayers/path"
 	"github.com/scionproto/scion/pkg/slayers/path/scion"
 	"github.com/scionproto/scion/private/topology"
+	"golang.org/x/net/ipv4"
+
+	"verification/dependencies/encoding/binary"
+	"verification/io"
+	sl "verification/utils/slices"
 	. "verification/utils/definitions"
 )
 
@@ -652,3 +654,13 @@ pure func (d *DataPlane) DpAgreesWithSpec(dp io.DataPlaneSpec) bool {
 		d.dpSpecWellConfiguredNeighborIAs(dp) &&
 		d.dpSpecWellConfiguredLinkTypes(dp)
 }
+
+ghost
+requires dp.Valid()
+requires acc(msg.Mem(), R50)
+decreases
+pure func MsgToAbsVal(dp io.DataPlaneSpec, msg *ipv4.Message, ingressID uint16) (res io.IO_val) {
+	return unfolding acc(msg.Mem(), R50) in
+		absIO_val(dp, msg.Buffers[0], ingressID)
+}
+
diff --git a/router/widen-lemma.gobra b/router/widen-lemma.gobra
new file mode 100644
index 000000000..e000c6a11
--- /dev/null
+++ b/router/widen-lemma.gobra
@@ -0,0 +1,970 @@
+// Copyright 2022 ETH Zurich
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +gobra
+
+package router
+
+import (
+	sl "verification/utils/slices"
+	"verification/io"
+	. "verification/utils/definitions"
+	"verification/dependencies/encoding/binary"
+	"github.com/scionproto/scion/pkg/slayers/path"
+	"github.com/scionproto/scion/pkg/slayers/path/scion"
+)
+
+// Some thins in this file can be simplified. Nonetheless, the important definition here
+// is absIO_valWidenLemma. Everything else can be seen as an implementation detail.
+
+ghost
+requires  0 <= length && length <= len(raw)
+requires  acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R49)
+requires  acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R49)
+preserves dp.Valid()
+ensures   acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R49)
+ensures   acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R49)
+ensures   absIO_val(dp, raw[:length], ingressID).isIO_val_Pkt2 ==>
+	absIO_val(dp, raw[:length], ingressID) == absIO_val(dp, raw, ingressID)
+decreases
+func absIO_valWidenLemma(dp io.DataPlaneSpec, raw []byte, ingressID uint16, length int) {
+	var ret1 io.IO_val
+	var ret2 io.IO_val
+
+	if (validPktMetaHdr(raw[:length]) && absPkt(dp, raw[:length]) != none[io.IO_pkt2]) {
+		validPktMetaHdrWidenLemma(raw, length)
+		assert validPktMetaHdr(raw)
+		absPktWidenLemma(dp, raw, length)
+		assert absPkt(dp, raw) != none[io.IO_pkt2]
+
+		ret1 = io.IO_val(io.IO_val_Pkt2{ifsToIO_ifs(ingressID), get(absPkt(dp, raw))})
+		ret2 = io.IO_val(io.IO_val_Pkt2{ifsToIO_ifs(ingressID), get(absPkt(dp, raw[:length]))})
+		assert ret1 == reveal absIO_val(dp, raw, ingressID)
+		assert ret2 == reveal absIO_val(dp, raw[:length], ingressID)
+		assert ret1 == ret2
+		assert absIO_val(dp, raw[:length], ingressID).isIO_val_Pkt2 ==>
+			absIO_val(dp, raw[:length], ingressID) == absIO_val(dp, raw, ingressID)
+	} else {
+		assert !(reveal absIO_val(dp, raw[:length], ingressID).isIO_val_Pkt2)
+	}
+}
+
+ghost
+requires 0 <= length && length <= len(raw)
+requires acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R51)
+requires acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R51)
+requires validPktMetaHdr(raw[:length])
+ensures  acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R51)
+ensures  acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R51)
+ensures  validPktMetaHdr(raw)
+decreases
+func validPktMetaHdrWidenLemma(raw []byte, length int) {
+	unfold acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R56)
+	unfold acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R56)
+	reveal validPktMetaHdr(raw[:length])
+	ret1 := reveal validPktMetaHdr(raw)
+	ret2 := reveal validPktMetaHdr(raw[:length])
+	assert ret1 == ret2
+	fold acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R56)
+	fold acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R56)
+}
+
+ghost
+requires  0 <= length && length <= len(raw)
+requires dp.Valid()
+requires acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R50)
+requires acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R50)
+requires validPktMetaHdr(raw)
+requires validPktMetaHdr(raw[:length])
+ensures  acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R50)
+ensures  acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R50)
+ensures  validPktMetaHdr(raw)
+ensures  validPktMetaHdr(raw[:length])
+ensures  absPkt(dp, raw) == absPkt(dp, raw[:length])
+decreases
+func absPktWidenLemma(dp io.DataPlaneSpec, raw []byte, length int) {
+
+	// declarations
+	var last1 io.IO_as
+	var last2 io.IO_as
+	var first1 io.IO_as
+	var first2 io.IO_as
+	var leftAsidSeq1 option[seq[io.IO_as]]
+	var leftAsidSeq2 option[seq[io.IO_as]]
+	var rightAsidSeq1 option[seq[io.IO_as]]
+	var rightAsidSeq2 option[seq[io.IO_as]]
+	var midAsidSeq1 option[seq[io.IO_as]]
+	var midAsidSeq2 option[seq[io.IO_as]]
+	var midAsid1 option[io.IO_as]
+	var midAsid2 option[io.IO_as]
+	var ret1 option[io.IO_pkt2]
+	var ret2 option[io.IO_pkt2]
+	var lm bool
+
+	// abspkt step by step
+	_ := reveal validPktMetaHdr(raw)
+	_ := reveal validPktMetaHdr(raw[:length])
+	hdr1 := unfolding acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R51) in binary.BigEndian.Uint32(raw[0:4])
+	hdr2 := unfolding acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R51) in binary.BigEndian.Uint32(raw[:length][0:4])
+	assert unfolding acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R51) in binary.BigEndian.Uint32(raw[:length][0:4]) == unfolding acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R51) in binary.BigEndian.Uint32(raw[:length][0:4])
+	assert hdr1 == hdr2
+
+	metaHdr1 := scion.DecodedFrom(hdr1)
+	metaHdr2 := scion.DecodedFrom(hdr2)
+	assert metaHdr1 == metaHdr2
+
+	currINFIdx1 := int(metaHdr1.CurrINF)
+	currINFIdx2 := int(metaHdr2.CurrINF)
+	assert currINFIdx1 == currINFIdx2
+
+	currHFIdx1 := int(metaHdr1.CurrHF)
+	currHFIdx2 := int(metaHdr2.CurrHF)
+	assert currHFIdx1 == currHFIdx2
+
+	seg1Len1 := int(metaHdr1.SegLen[0])
+	seg1Len2 := int(metaHdr2.SegLen[0])
+	assert seg1Len1 == seg1Len2
+
+	seg2Len1 := int(metaHdr1.SegLen[1])
+	seg2Len2 := int(metaHdr2.SegLen[1])
+	assert seg2Len1 == seg2Len2
+
+	seg3Len1 := int(metaHdr1.SegLen[2])
+	seg3Len2 := int(metaHdr2.SegLen[2])
+	assert seg3Len1 == seg3Len2
+
+	segLen1 := lengthOfCurrSeg(currHFIdx1, seg1Len1, seg2Len1, seg3Len1)
+	segLen2 := lengthOfCurrSeg(currHFIdx2, seg1Len2, seg2Len2, seg3Len2)
+	assert segLen1 == segLen2
+
+	prevSegLen1 := lengthOfPrevSeg(currHFIdx1, seg1Len1, seg2Len1, seg3Len1)
+	prevSegLen2 := lengthOfPrevSeg(currHFIdx2, seg1Len2, seg2Len2, seg3Len2)
+	assert prevSegLen1 == prevSegLen2
+
+	numINF1 := numInfoFields(seg1Len1, seg2Len1, seg3Len1)
+	numINF2 := numInfoFields(seg1Len2, seg2Len2, seg3Len2)
+	assert numINF1 == numINF2
+
+	offset1 := hopFieldOffset(numINF1, 0)
+	offset2 := hopFieldOffset(numINF2, 0)
+	assert offset1 == offset2
+
+	consDir1 := path.ConsDir(raw, currINFIdx1)
+	consDir2 := path.ConsDir(raw[:length], currINFIdx2)
+	consDirWidenLemma(raw, length, currINFIdx1)
+	assert consDir1 == consDir2
+
+	asidForCurrSegWidenLemma(dp, raw, numINF1, currHFIdx1, prevSegLen1+segLen1, prevSegLen1, consDir1, dp.Asid(), length)
+	currAsidSeq2 := asidForCurrSeg(dp, raw, numINF1, currHFIdx1, prevSegLen1+segLen1, prevSegLen1, consDir1, dp.Asid())
+	currAsidSeq1 := asidForCurrSeg(dp, raw[:length], numINF2, currHFIdx2, prevSegLen2+segLen2, prevSegLen2, consDir2, dp.Asid())
+	assert currAsidSeq1 == currAsidSeq2
+
+	if (currAsidSeq1 == none[seq[io.IO_as]]) {
+		ret := none[io.IO_pkt2]
+		assert ret == reveal absPkt(dp, raw)
+		assert ret == reveal absPkt(dp, raw[:length])
+	} else {
+
+		last1 = get(currAsidSeq1)[segLen1-1]
+		last2 = get(currAsidSeq2)[segLen1-1]
+		assert last1 == last2
+
+		first1 = get(currAsidSeq1)[0]
+		first2 = get(currAsidSeq2)[0]
+		assert first1 == first2
+
+		asidsForLeftSegWidenLemma(dp, raw, numINF1, currINFIdx1+1, seg1Len1, seg2Len1, seg3Len1, last1, length)
+		leftAsidSeq1 = asidsForLeftSeg(dp, raw, numINF1, currINFIdx1 + 1, seg1Len1, seg2Len1, seg3Len1, last1)
+		leftAsidSeq2 = asidsForLeftSeg(dp, raw[:length], numINF2, currINFIdx2 + 1, seg1Len2, seg2Len2, seg3Len2, last2)
+		assert leftAsidSeq1 == leftAsidSeq2
+
+		asidsForRightSegWidenLemma(dp, raw, numINF1, currINFIdx1-1, seg1Len1, seg2Len1, seg3Len1, first1, length)
+		rightAsidSeq1 = asidsForRightSeg(dp, raw, numINF1, currINFIdx1 - 1, seg1Len1, seg2Len1, seg3Len1, first1)
+		rightAsidSeq2 = asidsForRightSeg(dp, raw[:length], numINF2, currINFIdx2 - 1, seg1Len2, seg2Len2, seg3Len2, first2)
+		assert rightAsidSeq1 == rightAsidSeq2
+
+		if (leftAsidSeq1 == none[seq[io.IO_as]] || rightAsidSeq1 == none[seq[io.IO_as]]) {
+			ret := none[io.IO_pkt2]
+			assert ret == reveal absPkt(dp, raw)
+			assert ret == reveal absPkt(dp, raw[:length])
+		} else {
+			assert leftAsidSeq2 != none[seq[io.IO_as]] && rightAsidSeq2 != none[seq[io.IO_as]]
+
+			midAsid1 = ((currINFIdx1 == 0 && seg2Len1 > 0 && seg3Len1 > 0) ? some(get(leftAsidSeq1)[len(get(leftAsidSeq1))-1]) : (currINFIdx1 == 2 && seg2Len1 > 0) ? some(get(rightAsidSeq1)[0]) : none[io.IO_as])
+			midAsid2 = ((currINFIdx2 == 0 && seg2Len2 > 0 && seg3Len2 > 0) ? some(get(leftAsidSeq2)[len(get(leftAsidSeq2))-1]) : (currINFIdx2 == 2 && seg2Len2 > 0) ? some(get(rightAsidSeq2)[0]) : none[io.IO_as])
+			assert midAsid1 == midAsid2
+
+			asidsForMidSegWidenLemma(dp, raw, numINF1, currINFIdx1+2, seg1Len1, seg2Len1, seg3Len1, midAsid1, length)
+			midAsidSeq1 = asidsForMidSeg(dp, raw, numINF1, currINFIdx1 + 2, seg1Len1, seg2Len1, seg3Len1, midAsid1)
+			midAsidSeq2 = asidsForMidSeg(dp, raw[:length], numINF2, currINFIdx2 + 2, seg1Len2, seg2Len2, seg3Len2, midAsid2)
+			assert midAsidSeq1 == midAsidSeq2
+			if (midAsidSeq1 == none[seq[io.IO_as]]) {
+				ret := none[io.IO_pkt2]
+				assert ret == reveal absPkt(dp, raw)
+				assert ret == reveal absPkt(dp, raw[:length])
+			} else {
+				currSegWidenLemma(raw, offset1+prevSegLen1, currINFIdx1, currHFIdx1-prevSegLen1, get(currAsidSeq1), length)
+				leftSegWidenLemma(raw, currINFIdx1 + 1, seg1Len1, seg2Len1, seg3Len1, get(leftAsidSeq1), length)
+				midSegWidenLemma(raw, currINFIdx1 + 2, seg1Len1, seg2Len1, seg3Len1, get(midAsidSeq1), length)
+				rightSegWidenLemma(raw, currINFIdx1 - 1, seg1Len1, seg2Len1, seg3Len1, get(rightAsidSeq1), length)
+				ret1 = some(io.IO_pkt2(io.IO_Packet2{
+					CurrSeg : currSeg(raw, offset1+prevSegLen1, currINFIdx1, currHFIdx1-prevSegLen1, get(currAsidSeq1)),
+					LeftSeg : leftSeg(raw, currINFIdx1 + 1, seg1Len1, seg2Len1 , seg3Len1, get(leftAsidSeq1)),
+					MidSeg : midSeg(raw, currINFIdx1 + 2, seg1Len1, seg2Len1 , seg3Len1, get(midAsidSeq1)),
+					RightSeg : rightSeg(raw, currINFIdx1 - 1, seg1Len1, seg2Len1 , seg3Len1, get(rightAsidSeq1)),
+				}))
+				ret2 = some(io.IO_pkt2(io.IO_Packet2{
+					CurrSeg : currSeg(raw[:length], offset2+prevSegLen2, currINFIdx2, currHFIdx2-prevSegLen2, get(currAsidSeq2)),
+					LeftSeg : leftSeg(raw[:length], currINFIdx2 + 1, seg1Len2, seg2Len2 , seg3Len2, get(leftAsidSeq2)),
+					MidSeg : midSeg(raw[:length], currINFIdx2 + 2, seg1Len2, seg2Len2 , seg3Len2, get(midAsidSeq2)),
+					RightSeg : rightSeg(raw[:length], currINFIdx2 - 1, seg1Len2, seg2Len2 , seg3Len2, get(rightAsidSeq2)),
+				}))
+				reveal absPkt(dp, raw)
+				reveal absPkt(dp, raw[:length])
+				assert ret1 == absPkt(dp, raw)
+				assert ret2 == absPkt(dp, raw[:length])
+				assert ret1 == ret2
+			}
+		}
+	}
+}
+
+ghost
+requires  0 <= length && length <= len(raw)
+requires acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R55)
+requires acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R55)
+requires 0 <= currINFIdx
+requires path.InfoFieldOffset(currINFIdx) < length
+ensures  acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R55)
+ensures  acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R55)
+ensures  path.ConsDir(raw, currINFIdx) == path.ConsDir(raw[:length], currINFIdx)
+decreases
+func consDirWidenLemma(raw []byte, length int, currINFIdx int) {
+	unfold acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R56)
+	unfold acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R56)
+	assert &raw[path.InfoFieldOffset(currINFIdx)] == &raw[:length][path.InfoFieldOffset(currINFIdx)]
+	assert raw[path.InfoFieldOffset(currINFIdx)] == raw[:length][path.InfoFieldOffset(currINFIdx)]
+	assert (raw[path.InfoFieldOffset(currINFIdx)] & 0x1 == 0x1) == (raw[:length][path.InfoFieldOffset(currINFIdx)] & 0x1 == 0x1)
+	fold acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R56)
+	fold acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R56)
+}
+
+ghost
+requires 0 <= length && length <= len(raw)
+requires 1 <= numINF1
+requires 0 <= prevSegLen1 && prevSegLen1 <= currHFIdx1
+requires currHFIdx1 < segLen1
+requires hopFieldOffset(numINF1, segLen1) <= length
+requires dp.Valid()
+requires acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R52)
+requires acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R52)
+ensures  acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R52)
+ensures  acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R52)
+ensures  asidForCurrSeg(dp, raw, numINF1, currHFIdx1, segLen1, prevSegLen1, consDir1, asid1) ==
+	asidForCurrSeg(dp, raw[:length], numINF1, currHFIdx1, segLen1, prevSegLen1, consDir1, asid1)
+decreases
+func asidForCurrSegWidenLemma(
+	dp io.DataPlaneSpec,
+	raw []byte,
+	numINF1 int,
+	currHFIdx1 int,
+	segLen1 int,
+	prevSegLen1 int,
+	consDir1 bool,
+	asid1 io.IO_as,
+	length int) {
+
+	var ret1 option[seq[io.IO_as]]
+	var ret2 option[seq[io.IO_as]]
+	var left1 option[seq[io.IO_as]]
+	var left2 option[seq[io.IO_as]]
+	var right1 option[seq[io.IO_as]]
+	var right2 option[seq[io.IO_as]]
+
+
+	if (segLen1 == 0) {
+		assert segLen1 == 0
+		ret1 = some(seq[io.IO_as]{})
+		ret2 = some(seq[io.IO_as]{})
+		assert ret1 == asidForCurrSeg(dp, raw, numINF1, currHFIdx1, segLen1, prevSegLen1, consDir1, asid1)
+		assert ret2 == asidForCurrSeg(dp, raw[:length], numINF1, currHFIdx1, segLen1, prevSegLen1, consDir1, asid1)
+		assert ret1 == ret2
+	} else {
+		asidsBeforeWidenLemma(dp, raw, numINF1, numINF1, currHFIdx1, currHFIdx1, prevSegLen1, prevSegLen1, consDir1, consDir1, asid1, asid1, length)
+		left1 = asidsBefore(dp, raw, numINF1, currHFIdx1, prevSegLen1, consDir1, asid1)
+		left2 = asidsBefore(dp, raw[:length], numINF1, currHFIdx1, prevSegLen1, consDir1, asid1)
+		assert left1 == left2
+		newP := (R52 + R53)/2
+		asidsAfterWidenLemma(dp, raw, numINF1, currHFIdx1, segLen1, consDir1, asid1, length, newP)
+		right1 = asidsAfter(dp, raw, numINF1, currHFIdx1, segLen1, consDir1, asid1)
+		right2 = asidsAfter(dp, raw[:length], numINF1, currHFIdx1, segLen1, consDir1, asid1)
+		assert right1 == right2
+		if (left1 == none[seq[io.IO_as]] || right1 == none[seq[io.IO_as]]) {
+			assert (left2 == none[seq[io.IO_as]] || right2 == none[seq[io.IO_as]])
+			ret1 = none[seq[io.IO_as]]
+			ret2 = none[seq[io.IO_as]]
+			assert ret1 == reveal asidForCurrSeg(dp, raw, numINF1, currHFIdx1, segLen1, prevSegLen1, consDir1, asid1)
+			assert ret2 == reveal asidForCurrSeg(dp, raw[:length], numINF1, currHFIdx1, segLen1, prevSegLen1, consDir1, asid1)
+			assert ret1 == ret2
+		} else {
+			assert (left2 != none[seq[io.IO_as]] && right2 != none[seq[io.IO_as]])
+			ret1 = some(get(left1) ++ get(right1)[1:])
+			ret2 = some(get(left2) ++ get(right2)[1:])
+			assert ret1 == reveal asidForCurrSeg(dp, raw, numINF1, currHFIdx1, segLen1, prevSegLen1, consDir1, asid1)
+			assert ret2 == reveal asidForCurrSeg(dp, raw[:length], numINF1, currHFIdx1, segLen1, prevSegLen1, consDir1, asid1)
+			assert ret1 == ret2
+		}
+	}
+	assert ret1 == reveal asidForCurrSeg(dp, raw, numINF1, currHFIdx1, segLen1, prevSegLen1, consDir1, asid1)
+	assert ret2 == reveal asidForCurrSeg(dp, raw[:length], numINF1, currHFIdx1, segLen1, prevSegLen1, consDir1, asid1)
+	assert ret1 == ret2
+}
+
+ghost
+requires 1 <= numINF1
+requires 0 <= prevSegLen1 && prevSegLen1 <= currHFIdx1
+requires length <= len(raw)
+requires hopFieldOffset(numINF1, currHFIdx1) + path.HopLen <= length
+requires dp.Valid()
+requires consDir1 == consDir2
+requires prevSegLen1 == prevSegLen2
+requires currHFIdx1 == currHFIdx2
+requires numINF1 == numINF2
+requires asid1 == asid2
+requires acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R53)
+requires acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R53)
+ensures  acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R53)
+ensures  acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R53)
+ensures  forall i int :: { &raw[i] } 0 <= i && i < len(raw) ==> old(unfolding acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R53) in raw[i]) == (unfolding acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R53) in raw[i])
+ensures  forall i int :: { &raw[:length][i] } 0 <= i && i < len(raw[:length]) ==> old(unfolding acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R53) in raw[:length][i]) == (unfolding acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R53) in raw[:length][i])
+ensures  asidsBefore(dp, raw, numINF1, currHFIdx1, prevSegLen1, consDir1, asid1) ==
+		 asidsBefore(dp, raw[:length], numINF2, currHFIdx2, prevSegLen2, consDir2, asid2)
+decreases currHFIdx1 - prevSegLen1
+func asidsBeforeWidenLemma(
+	dp io.DataPlaneSpec,
+	raw []byte,
+	numINF1 int,
+	numINF2 int,
+	currHFIdx1 int,
+	currHFIdx2 int,
+	prevSegLen1 int,
+	prevSegLen2 int,
+	consDir1 bool,
+	consDir2 bool,
+	asid1 io.IO_as,
+	asid2 io.IO_as,
+	length int) {
+
+	var ret1 option[seq[io.IO_as]]
+	var ret2 option[seq[io.IO_as]]
+	var nextAsid1 option[io.IO_as]
+	var nextAsid2 option[io.IO_as]
+	var nextAsidSeq1 option[seq[io.IO_as]]
+	var nextAsidSeq2 option[seq[io.IO_as]]
+
+	if (currHFIdx1 == prevSegLen1) {
+		assert currHFIdx2 == prevSegLen2
+		ret1 = some(seq[io.IO_as]{asid1})
+		ret2 = some(seq[io.IO_as]{asid2})
+		assert ret1 == ret2
+	} else {
+		assert currHFIdx2 != prevSegLen2
+		nextAsid1 = asidFromIfs(dp, raw, numINF1, currHFIdx1, !consDir1, asid1)
+		nextAsid2 = asidFromIfs(dp, raw[:length], numINF2, currHFIdx2, !consDir2, asid2)
+		asidFromIfsWidenLemma(dp, raw, numINF1, numINF2, currHFIdx1, currHFIdx2, !consDir1, !consDir2, asid1, asid2, length)
+		assert nextAsid1 == nextAsid2
+		if (nextAsid1 == none[io.IO_as]) {
+			assert nextAsid2 == none[io.IO_as]
+			ret1 = none[seq[io.IO_as]]
+			ret2 = none[seq[io.IO_as]]
+			assert ret1 == ret2
+			assert ret1 == asidsBefore(dp, raw,	numINF1, currHFIdx1, prevSegLen1, consDir1, asid1)
+			assert ret2 == asidsBefore(dp, raw[:length],	numINF2, currHFIdx2, prevSegLen2, consDir2, asid2)
+		} else {
+			assert nextAsid2 != none[io.IO_as]
+			asidsBeforeWidenLemma(dp, raw, numINF1, numINF2, currHFIdx1-1, currHFIdx2-1, prevSegLen1, prevSegLen2, consDir1, consDir2, get(nextAsid1), get(nextAsid2), length)
+			nextAsidSeq1 = asidsBefore(dp, raw, numINF1, currHFIdx1-1, prevSegLen1, consDir1, get(nextAsid1))
+			nextAsidSeq2 = asidsBefore(dp, raw[:length], numINF2, currHFIdx2-1, prevSegLen2, consDir2, get(nextAsid2))
+			assert nextAsidSeq1 == nextAsidSeq2
+			if (nextAsidSeq1 == none[seq[io.IO_as]]) {
+				assert nextAsidSeq2 == none[seq[io.IO_as]]
+				ret1 = none[seq[io.IO_as]]
+				ret2 = none[seq[io.IO_as]]
+				assert ret1 == ret2
+				assert ret1 == asidsBefore(dp, raw,	numINF1, currHFIdx1, prevSegLen1, consDir1, asid1)
+				assert ret2 == asidsBefore(dp, raw[:length],	numINF2, currHFIdx2, prevSegLen2, consDir2, asid2)
+			} else {
+				ret1 = some(get(nextAsidSeq1) ++ seq[io.IO_as]{asid1})
+				ret2 = some(get(nextAsidSeq2) ++ seq[io.IO_as]{asid2})
+				assert ret1 == ret2
+				assert ret1 == asidsBefore(dp, raw,	numINF1, currHFIdx1, prevSegLen1, consDir1, asid1)
+				assert ret2 == asidsBefore(dp, raw[:length],	numINF2, currHFIdx2, prevSegLen2, consDir2, asid2)
+			}
+		}
+	}
+}
+
+ghost
+requires 1 <= numINF1
+requires 0 <= currHFIdx1
+requires numINF1 == numINF2
+requires currHFIdx1 == currHFIdx2
+requires consDir1 == consDir2
+requires asid1 == asid2
+requires 0 <= length && length <= len(raw)
+requires hopFieldOffset(numINF1, currHFIdx1) + path.HopLen <= length
+requires dp.Valid()
+requires acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R54)
+requires acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R54)
+ensures  acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R54)
+ensures  acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R54)
+ensures  asidFromIfs(dp, raw, numINF1, currHFIdx1, consDir1, asid1) ==
+		 asidFromIfs(dp, raw[:length], numINF2, currHFIdx2, consDir2, asid2)
+decreases
+func asidFromIfsWidenLemma(
+	dp io.DataPlaneSpec,
+	raw []byte,
+	numINF1 int,
+	numINF2 int,
+	currHFIdx1 int,
+	currHFIdx2 int,
+	consDir1 bool,
+	consDir2 bool,
+	asid1 io.IO_as,
+	asid2 io.IO_as,
+	length int) {
+	var ret1 option[io.IO_as]
+	var ret2 option[io.IO_as]
+
+	idx1 := hopFieldOffset(numINF1, currHFIdx1)
+	idx2 := hopFieldOffset(numINF2, currHFIdx1)
+	assert idx1 == idx2
+	unfold acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R55)
+	unfold acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R55)
+	assert forall i int :: { &raw[idx1+2+i] } { &raw[idx1+2:idx1+4][i] } 0 <= i && i < 2 ==>
+		&raw[idx1+2+i] == &raw[idx1+2:idx1+4][i]
+	assert forall i int :: { &raw[:length][idx2+2+i] } { &raw[:length][idx2+2:idx2+4][i] } 0 <= i && i < 2 ==>
+		&raw[:length][idx2+2+i] == &raw[:length][idx2+2:idx2+4][i]
+	assert forall i int :: { &raw[idx1+4+i] } { &raw[idx1+4:idx1+6][i] } 0 <= i && i < 2 ==>
+		&raw[idx1+4+i] == &raw[idx1+4:idx1+6][i]
+	assert forall i int :: { &raw[:length][idx2+4+i] } { &raw[idx2+4:idx2+6][i] } 0 <= i && i < 2 ==>
+		&raw[:length][idx2+4+i] == &raw[:length][idx2+4:idx2+6][i]
+	ifs1 := consDir1 ? binary.BigEndian.Uint16(raw[idx1+4:idx1+6]) : binary.BigEndian.Uint16(raw[idx1+2:idx1+4])
+	ifs2 := consDir2 ? binary.BigEndian.Uint16(raw[:length][idx2+4:idx2+6]) : binary.BigEndian.Uint16(raw[:length][idx2+2:idx2+4])
+	assert ifs1 == ifs2
+	asIfPair1 := io.AsIfsPair{asid1, io.IO_ifs(ifs1)}
+	asIfPair2 := io.AsIfsPair{asid2, io.IO_ifs(ifs2)}
+	assert asIfPair1 == asIfPair2
+	if (asIfPair1 in domain(dp.GetLinks())) {
+		assert asIfPair2 in domain(dp.GetLinks())
+		ret1 = some(dp.Lookup(asIfPair1).asid)
+		ret2 = some(dp.Lookup(asIfPair2).asid)
+		assert ret1 == ret2
+		assert ret1 == asidFromIfs(dp, raw, numINF1, currHFIdx1, consDir1, asid1)
+		assert ret2 == asidFromIfs(dp, raw[:length], numINF2, currHFIdx2, consDir2, asid2)
+	} else {
+		assert !(asIfPair2 in domain(dp.GetLinks()))
+		ret1 = none[io.IO_as]
+		ret2 = none[io.IO_as]
+		assert ret1 == ret2
+		assert ret1 == asidFromIfs(dp, raw, numINF1, currHFIdx1, consDir1, asid1)
+		assert ret2 == asidFromIfs(dp, raw[:length], numINF2, currHFIdx2, consDir2, asid2)
+	}
+	fold acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R55)
+	fold acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R55)
+	assert ret1 == ret2
+	assert ret1 == asidFromIfs(dp, raw, numINF1, currHFIdx1, consDir1, asid1)
+	assert ret2 == asidFromIfs(dp, raw[:length], numINF2, currHFIdx2, consDir2, asid2)
+}
+
+// --- The file has been simplified past this point
+
+ghost
+requires  R53 < p
+requires  1 <= numINF
+requires  0 <= currHFIdx && currHFIdx < segLen
+requires  length <= len(raw)
+requires  hopFieldOffset(numINF, segLen) <= length
+requires  dp.Valid()
+preserves acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), p)
+preserves acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), p)
+ensures   asidsAfter(dp, raw, numINF, currHFIdx, segLen, consDir, asid) ==
+	asidsAfter(dp, raw[:length], numINF, currHFIdx, segLen, consDir, asid)
+decreases segLen - currHFIdx + 1
+func asidsAfterWidenLemma(dp io.DataPlaneSpec, raw []byte, numINF int, currHFIdx int, segLen int, consDir bool, asid io.IO_as, length int, p perm) {
+	if currHFIdx != segLen - 1 {
+		nextAsid1 := asidFromIfs(dp, raw, numINF, currHFIdx, consDir, asid)
+		nextAsid2 := asidFromIfs(dp, raw[:length], numINF, currHFIdx, consDir, asid)
+		asidFromIfsWidenLemma(dp, raw, numINF, numINF, currHFIdx, currHFIdx, consDir, consDir, asid, asid, length)
+		assert nextAsid1 == nextAsid2
+		if nextAsid1 == none[io.IO_as] {
+			ret := none[seq[io.IO_as]]
+			assert ret == asidsAfter(dp, raw, numINF, currHFIdx, segLen, consDir, asid)
+			assert ret == asidsAfter(dp, raw[:length], numINF, currHFIdx, segLen, consDir, asid)
+		} else {
+			newP := (p + R53)/2
+			asidsAfterWidenLemma(dp, raw, numINF, currHFIdx+1, segLen, consDir, get(nextAsid1), length, newP)
+			nextAsidSeq1 := asidsAfter(dp, raw, numINF, currHFIdx+1, segLen, consDir, get(nextAsid1))
+			nextAsidSeq2 := asidsAfter(dp, raw[:length], numINF, currHFIdx+1, segLen, consDir, get(nextAsid2))
+			assert nextAsidSeq1 == nextAsidSeq2
+			if nextAsidSeq1 == none[seq[io.IO_as]] {
+				ret := none[seq[io.IO_as]]
+				assert ret == asidsAfter(dp, raw, numINF, currHFIdx, segLen, consDir, asid)
+				assert ret == asidsAfter(dp, raw[:length], numINF, currHFIdx, segLen, consDir, asid)
+			} else {
+				ret := some(seq[io.IO_as]{asid} ++ get(nextAsidSeq1))
+				assert ret == asidsAfter(dp, raw, numINF, currHFIdx, segLen, consDir, asid)
+				assert ret == asidsAfter(dp, raw[:length], numINF, currHFIdx, segLen, consDir, asid)
+			}
+		}
+	}
+}
+
+ghost
+requires  dp.Valid()
+requires  1 <= numINF
+requires  0 < seg1Len
+requires  0 <= seg2Len
+requires  0 <= seg3Len
+requires  0 <= length && length <= len(raw)
+requires  hopFieldOffset(numINF, seg1Len + seg2Len + seg3Len) <= length
+requires  currINFIdx <= numINF + 1
+requires  1 <= currINFIdx && currINFIdx < 4
+preserves acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R51)
+preserves acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R51)
+ensures   asidsForLeftSeg(dp, raw, numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid) ==
+	asidsForLeftSeg(dp, raw[:length], numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+decreases
+func asidsForLeftSegWidenLemma(dp io.DataPlaneSpec, raw []byte, numINF int, currINFIdx int, seg1Len int, seg2Len int, seg3Len int, asid io.IO_as, length int) {
+	consDir1 := path.ConsDir(raw, currINFIdx)
+	consDir2 := path.ConsDir(raw[:length], currINFIdx)
+	consDirWidenLemma(raw, length, currINFIdx)
+	assert consDir1 == consDir2
+
+	if currINFIdx == 1 && seg2Len > 0 {
+		asidForCurrSegWidenLemma(dp, raw, numINF, seg1Len, seg1Len+seg2Len, seg1Len, consDir1, asid, length)
+		ret1 := asidForCurrSeg(dp, raw, numINF, seg1Len, seg1Len+seg2Len, seg1Len, consDir1, asid)
+		ret2 := asidForCurrSeg(dp, raw[:length], numINF, seg1Len, seg1Len+seg2Len, seg1Len, consDir2, asid)
+		assert ret1 == reveal asidsForLeftSeg(dp, raw, numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret2 == reveal asidsForLeftSeg(dp, raw[:length], numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret1 == ret2
+	} else if currINFIdx == 2 && seg2Len > 0 && seg3Len > 0 {
+		asidForCurrSegWidenLemma(dp, raw, numINF, seg1Len+seg2Len, seg1Len+seg2Len+seg3Len, seg1Len+seg2Len, consDir1, asid, length)
+		ret1 := asidForCurrSeg(dp, raw, numINF, seg1Len+seg2Len, seg1Len+seg2Len+seg3Len, seg1Len+seg2Len, consDir1, asid)
+		ret2 := asidForCurrSeg(dp, raw[:length], numINF, seg1Len+seg2Len, seg1Len+seg2Len+seg3Len, seg1Len+seg2Len, consDir2, asid)
+		assert ret1 == reveal asidsForLeftSeg(dp, raw, numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret2 == reveal asidsForLeftSeg(dp, raw[:length], numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret1 == ret2
+	} else {
+		ret := some(seq[io.IO_as]{})
+		assert ret == reveal asidsForLeftSeg(dp, raw, numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret == reveal asidsForLeftSeg(dp, raw[:length], numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+	}
+}
+
+ghost
+requires  dp.Valid()
+requires  1 <= numINF
+requires  0 < seg1Len
+requires  0 <= seg2Len
+requires  0 <= seg3Len
+requires  0 <= length && length <= len(raw)
+requires  hopFieldOffset(numINF, seg1Len + seg2Len + seg3Len) <= length
+requires  currINFIdx <= numINF + 1
+requires  -1 <= currINFIdx && currINFIdx < 2
+preserves acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R51)
+preserves acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R51)
+ensures asidsForRightSeg(dp, raw, numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid) ==
+	asidsForRightSeg(dp, raw[:length], numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+decreases
+func asidsForRightSegWidenLemma(dp io.DataPlaneSpec, raw []byte, numINF int, currINFIdx int, seg1Len int, seg2Len int,seg3Len int, asid io.IO_as, length int) {
+	if currINFIdx == 1 && seg2Len > 0 {
+		consDir1 := path.ConsDir(raw, currINFIdx)
+		consDir2 := path.ConsDir(raw[:length], currINFIdx)
+		consDirWidenLemma(raw, length, currINFIdx)
+		assert consDir1 == consDir2
+		asidForCurrSegWidenLemma(dp, raw, numINF, seg1Len+seg2Len-1, seg1Len+seg2Len, seg1Len, consDir1, asid, length)
+		ret1 := asidForCurrSeg(dp, raw, numINF, seg1Len+seg2Len-1, seg1Len+seg2Len, seg1Len, consDir1, asid)
+		ret2 := asidForCurrSeg(dp, raw[:length], numINF, seg1Len+seg2Len-1, seg1Len+seg2Len, seg1Len, consDir2, asid)
+		assert ret1 == reveal asidsForRightSeg(dp, raw, numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret2 == reveal asidsForRightSeg(dp, raw[:length], numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret1 == ret2
+	} else if currINFIdx == 0 {
+		consDir1 := path.ConsDir(raw, currINFIdx)
+		consDir2 := path.ConsDir(raw[:length], currINFIdx)
+		consDirWidenLemma(raw, length, currINFIdx)
+		assert consDir1 == consDir2
+		asidForCurrSegWidenLemma(dp, raw, numINF, seg1Len-1, seg1Len, 0, consDir1, asid, length)
+		ret1 := asidForCurrSeg(dp, raw, numINF, seg1Len-1, seg1Len, 0, consDir1, asid)
+		ret2 := asidForCurrSeg(dp, raw[:length], numINF, seg1Len-1, seg1Len, 0, consDir2, asid)
+		assert ret1 == reveal asidsForRightSeg(dp, raw, numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret2 == reveal asidsForRightSeg(dp, raw[:length], numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret1 == ret2
+	} else {
+		ret := some(seq[io.IO_as]{})
+		assert ret == reveal asidsForRightSeg(dp, raw, numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret == reveal asidsForRightSeg(dp, raw[:length], numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+	}
+}
+
+ghost
+requires  dp.Valid()
+requires  1 <= numINF
+requires  0 < seg1Len
+requires  0 <= seg2Len
+requires  0 <= seg3Len
+requires  0 <= length && length <= len(raw)
+requires  hopFieldOffset(numINF, seg1Len + seg2Len + seg3Len) <= length
+requires  currINFIdx <= numINF + 1
+requires  2 <= currINFIdx && currINFIdx < 5
+requires  (currINFIdx == 4 && seg2Len > 0) ==> asid != none[io.IO_as]
+requires  (currINFIdx == 2 && seg2Len > 0 && seg3Len > 0) ==> asid != none[io.IO_as]
+preserves acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R51)
+preserves acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R51)
+ensures   asidsForMidSeg(dp, raw, numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid) ==
+	asidsForMidSeg(dp, raw[:length], numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+decreases
+func asidsForMidSegWidenLemma(dp io.DataPlaneSpec, raw []byte, numINF int, currINFIdx int, seg1Len int, seg2Len int, seg3Len int, asid option[io.IO_as], length int) {
+	if currINFIdx == 4 && seg2Len > 0 {
+		consDir1 := path.ConsDir(raw, 1)
+		consDir2 := path.ConsDir(raw[:length], 1)
+		consDirWidenLemma(raw, length, 1)
+		assert consDir1 == consDir2
+		asidForCurrSegWidenLemma(dp, raw, numINF, seg1Len-1, seg1Len, 0, consDir1, get(asid), length)
+		ret1 := asidForCurrSeg(dp, raw, numINF, seg1Len-1, seg1Len, 0, consDir1, get(asid))
+		ret2 := asidForCurrSeg(dp, raw[:length], numINF, seg1Len-1, seg1Len, 0, consDir2, get(asid))
+		assert ret1 == reveal asidsForMidSeg(dp, raw, numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret2 == reveal asidsForMidSeg(dp, raw[:length], numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret1 == ret2
+	} else if currINFIdx == 2 && seg2Len > 0 && seg3Len > 0 {
+		consDir1 := path.ConsDir(raw, 2)
+		consDir2 := path.ConsDir(raw[:length], 2)
+		consDirWidenLemma(raw, length, 2)
+		assert consDir1 == consDir2
+		asidForCurrSegWidenLemma(dp, raw, numINF, seg1Len+seg2Len, seg1Len+seg2Len+seg3Len, seg1Len+seg2Len, consDir1, get(asid), length)
+		ret1 := asidForCurrSeg(dp, raw, numINF, seg1Len + seg2Len, seg1Len + seg2Len + seg3Len, seg1Len + seg2Len, consDir1, get(asid))
+		ret2 := asidForCurrSeg(dp, raw[:length], numINF, seg1Len + seg2Len, seg1Len + seg2Len + seg3Len, seg1Len + seg2Len, consDir2, get(asid))
+		assert ret1 == reveal asidsForMidSeg(dp, raw, numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret2 == reveal asidsForMidSeg(dp, raw[:length], numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret1 == ret2
+	} else {
+		ret := some(seq[io.IO_as]{})
+		assert ret == reveal asidsForMidSeg(dp, raw, numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret == reveal asidsForMidSeg(dp, raw[:length], numINF, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+	}
+}
+
+ghost
+requires  path.InfoFieldOffset(currINFIdx) + path.InfoLen <= offset
+requires  0 < len(asid)
+requires  0 <= length && length <= len(raw)
+requires  offset + path.HopLen * len(asid) <= length
+requires  0 <= currHFIdx && currHFIdx <= len(asid)
+requires  0 <= currINFIdx && currINFIdx < 3
+preserves acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R51)
+preserves acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R51)
+ensures   currSeg(raw, offset, currINFIdx, currHFIdx, asid) ==
+	currSeg(raw[:length], offset, currINFIdx, currHFIdx, asid)
+decreases
+func currSegWidenLemma(raw []byte, offset int, currINFIdx int, currHFIdx int, asid seq[io.IO_as], length int) {
+	unfold acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R53)
+	unfold acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R53)
+
+	ainfo1 := timestamp(raw, currINFIdx)
+	ainfo2 := timestamp(raw[:length], currINFIdx)
+	assert ainfo1 == ainfo2
+
+	consDir1 := path.ConsDir(raw, currINFIdx)
+	consDir2 := path.ConsDir(raw[:length], currINFIdx)
+	assert consDir1 == consDir2
+
+	peer1 := path.Peer(raw, currINFIdx)
+	peer2 := path.Peer(raw[:length], currINFIdx)
+	assert peer1 == peer2
+
+	segmentWidenLemma(raw, offset, currHFIdx, asid, ainfo1, consDir1, peer1, length)
+	ret1 := segment(raw, offset, currHFIdx, asid, ainfo1, consDir1, peer1)
+	ret2 := segment(raw[:length], offset, currHFIdx, asid, ainfo2, consDir2, peer2)
+	assert ret1 == reveal currSeg(raw, offset, currINFIdx, currHFIdx, asid)
+	assert ret2 == reveal currSeg(raw[:length], offset, currINFIdx, currHFIdx, asid)
+	assert ret1 == ret2
+
+	fold acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R53)
+	fold acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R53)
+}
+
+ghost
+requires 0 <= offset
+requires 0 < len(asid)
+requires 0 <= length && length <= len(raw)
+requires offset + path.HopLen * len(asid) <= length
+requires 0 <= currHFIdx && currHFIdx <= len(asid)
+requires acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R52)
+requires acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R52)
+ensures  acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R52)
+ensures  acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R52)
+ensures  segment(raw, offset, currHFIdx, asid, ainfo, consDir, peer) == segment(raw[:length], offset, currHFIdx, asid, ainfo, consDir, peer)
+decreases
+func segmentWidenLemma(raw []byte, offset int, currHFIdx int, asid seq[io.IO_as], ainfo io.IO_ainfo, consDir bool, peer bool, length int) {
+	newP := (R52 + R53)/2
+	assert R53 < newP && newP < R52
+	hopFieldsConsDirWidenLemma(raw, offset, 0, set[io.IO_msgterm]{}, asid, ainfo, length, newP)
+	hopFieldsNotConsDirWidenLemma(raw, offset, len(asid)-1, set[io.IO_msgterm]{}, asid, ainfo, length, newP)
+	hopfields1 := consDir ? hopFieldsConsDir(raw, offset, 0, set[io.IO_msgterm]{}, asid, ainfo) : hopFieldsNotConsDir(raw, offset, len(asid) - 1, set[io.IO_msgterm]{}, asid, ainfo)
+	hopfields2 := consDir ? hopFieldsConsDir(raw[:length], offset, 0, set[io.IO_msgterm]{}, asid, ainfo) : hopFieldsNotConsDir(raw[:length], offset, len(asid) - 1, set[io.IO_msgterm]{}, asid, ainfo)
+	assert hopfields1 == hopfields2
+
+	uinfo := uInfo(hopfields1, currHFIdx, consDir)
+
+	ret1 := io.IO_seg2(io.IO_seg3_{
+		AInfo :ainfo,
+		UInfo : uinfo,
+		ConsDir : consDir,
+		Peer : peer,
+		Past : segPast(hopfields1, currHFIdx - 1),
+		Future : segFuture(hopfields1, currHFIdx),
+		History : segHistory(hopfields1, currHFIdx - 1),
+	})
+	ret2 := io.IO_seg2(io.IO_seg3_{
+		AInfo :ainfo,
+		UInfo : uinfo,
+		ConsDir : consDir,
+		Peer : peer,
+		Past : segPast(hopfields2, currHFIdx - 1),
+		Future : segFuture(hopfields2, currHFIdx),
+		History : segHistory(hopfields2, currHFIdx - 1),
+	})
+	assert ret1 == segment(raw, offset, currHFIdx, asid, ainfo, consDir, peer)
+	assert ret2 == segment(raw[:length], offset, currHFIdx, asid, ainfo, consDir, peer)
+	assert ret1 == ret2
+}
+
+ghost
+requires  R53 < p
+requires  0 <= offset
+requires  0 <= currHFIdx && currHFIdx <= len(asid)
+requires  0 <= length && length <= len(raw)
+requires  offset + path.HopLen * len(asid) <= length
+preserves acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), p)
+preserves acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), p)
+ensures  hopFieldsConsDir(raw, offset, currHFIdx, beta, asid, ainfo) ==
+	hopFieldsConsDir(raw[:length], offset, currHFIdx, beta, asid, ainfo)
+decreases len(asid) - currHFIdx
+func hopFieldsConsDirWidenLemma(raw []byte, offset int, currHFIdx int, beta set[io.IO_msgterm], asid seq[io.IO_as], ainfo io.IO_ainfo, length int, p perm) {
+	if currHFIdx == len(asid) {
+		ret := seq[io.IO_HF]{}
+		assert ret == hopFieldsConsDir(raw, offset, currHFIdx, beta, asid, ainfo)
+		assert ret == hopFieldsConsDir(raw[:length], offset, currHFIdx, beta, asid, ainfo)
+	} else {
+		hopFieldWidenLemma(raw, offset + path.HopLen * currHFIdx, beta, asid[currHFIdx], ainfo, length)
+		hf1 := hopField(raw, offset + path.HopLen * currHFIdx, beta, asid[currHFIdx], ainfo)
+		hf2 := hopField(raw[:length], offset + path.HopLen * currHFIdx, beta, asid[currHFIdx], ainfo)
+		assert hf1 == hf2
+
+		newP := (p + R53)/2
+		assert R53 < newP && newP < p
+		hopFieldsConsDirWidenLemma(raw, offset, currHFIdx + 1, (beta union set[io.IO_msgterm]{hf1.HVF}), asid, ainfo, length, newP)
+		ret1 := seq[io.IO_HF]{hf1} ++ hopFieldsConsDir(raw, offset, currHFIdx + 1, (beta union set[io.IO_msgterm]{hf1.HVF}), asid, ainfo)
+		ret2 := seq[io.IO_HF]{hf2} ++ hopFieldsConsDir(raw[:length], offset, currHFIdx + 1, (beta union set[io.IO_msgterm]{hf2.HVF}), asid, ainfo)
+		assert ret1 == hopFieldsConsDir(raw, offset, currHFIdx, beta, asid, ainfo)
+		assert ret2 == hopFieldsConsDir(raw[:length], offset, currHFIdx, beta, asid, ainfo)
+		assert ret1 == ret2
+	}
+}
+
+ghost
+requires  0 <= length && length <= len(raw)
+requires  idx + path.HopLen <= length
+requires  0 <= idx
+preserves acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R54)
+preserves acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R54)
+ensures   hopField(raw, idx, beta, asid, ainfo) == hopField(raw[:length], idx, beta, asid, ainfo)
+decreases
+func hopFieldWidenLemma(raw []byte, idx int, beta set[io.IO_msgterm], asid io.IO_as, ainfo io.IO_ainfo, length int) {
+	unfold acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R55)
+	unfold acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R55)
+
+	assert forall i int :: { &raw[idx+2+i] } { &raw[idx+2:idx+4][i] } 0 <= i && i < 2 ==> &raw[idx+2+i] == &raw[idx+2:idx+4][i]
+	assert forall i int :: { &raw[idx+4+i] } { &raw[idx+4:idx+6][i] } 0 <= i && i < 2 ==> &raw[idx+4+i] == &raw[idx+4:idx+6][i]
+	inif21 := binary.BigEndian.Uint16(raw[idx+2:idx+4])
+	inif22 := binary.BigEndian.Uint16(raw[:length][idx+2:idx+4])
+	assert inif21 == inif22
+
+	egif2 := binary.BigEndian.Uint16(raw[idx+4:idx+6])
+	op_inif2 := inif21 == 0 ? none[io.IO_ifs] : some(io.IO_ifs(inif21))
+	op_egif2 := egif2 == 0 ? none[io.IO_ifs] : some(io.IO_ifs(egif2))
+	ts := io.IO_msgterm(io.MsgTerm_Num{ainfo})
+	l := io.IO_msgterm(io.MsgTerm_L{seq[io.IO_msgterm]{ts, io.if2term(op_inif2), io.if2term(op_egif2), io.IO_msgterm(io.MsgTerm_FS{beta})}})
+	hvf := io.mac(io.macKey(io.asidToKey(asid)), l)
+
+	ret1 := io.IO_HF(io.IO_HF_{
+		InIF2 : op_inif2,
+		EgIF2 : op_egif2,
+		HVF : hvf,
+	})
+	ret2 := io.IO_HF(io.IO_HF_{
+		InIF2 : op_inif2,
+		EgIF2 : op_egif2,
+		HVF : hvf,
+	})
+	assert ret1 == hopField(raw, idx, beta, asid, ainfo)
+	assert ret2 == hopField(raw[:length], idx, beta, asid, ainfo)
+	assert ret1 == ret2
+	fold acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R55)
+	fold acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R55)
+}
+
+ghost
+requires  R53 < p
+requires  0 <= offset
+requires  -1 <= currHFIdx && currHFIdx < len(asid)
+requires  0 <= length && length <= len(raw)
+requires  offset + path.HopLen * currHFIdx + path.HopLen <= length
+preserves acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), p)
+preserves acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), p)
+ensures   hopFieldsNotConsDir(raw, offset, currHFIdx, beta, asid, ainfo) ==
+	hopFieldsNotConsDir(raw[:length], offset, currHFIdx, beta, asid, ainfo)
+decreases currHFIdx + 1
+func hopFieldsNotConsDirWidenLemma(raw []byte, offset int, currHFIdx int, beta set[io.IO_msgterm], asid seq[io.IO_as], ainfo io.IO_ainfo, length int, p perm) {
+	if currHFIdx == -1 {
+		ret := seq[io.IO_HF]{}
+		assert ret == hopFieldsNotConsDir(raw, offset, currHFIdx, beta, asid, ainfo)
+		assert ret == hopFieldsNotConsDir(raw[:length], offset, currHFIdx, beta, asid, ainfo)
+	} else {
+		hopFieldWidenLemma(raw, offset + path.HopLen * currHFIdx, beta, asid[currHFIdx], ainfo, length)
+		hf1 := hopField(raw, offset + path.HopLen * currHFIdx, beta, asid[currHFIdx], ainfo)
+		hf2 := hopField(raw[:length], offset + path.HopLen * currHFIdx, beta, asid[currHFIdx], ainfo)
+		assert hf1 == hf2
+
+		newP := (p + R53)/2
+		assert R53 < newP && newP < p
+		hopFieldsNotConsDirWidenLemma(raw, offset, currHFIdx - 1, (beta union set[io.IO_msgterm]{hf1.HVF}), asid, ainfo, length, newP)
+		ret1 := hopFieldsNotConsDir(raw, offset, currHFIdx - 1, (beta union set[io.IO_msgterm]{hf1.HVF}), asid, ainfo) ++ seq[io.IO_HF]{hf1}
+		ret2 := hopFieldsNotConsDir(raw[:length], offset, currHFIdx - 1, (beta union set[io.IO_msgterm]{hf2.HVF}), asid, ainfo) ++ seq[io.IO_HF]{hf2}
+		assert ret1 == hopFieldsNotConsDir(raw, offset, currHFIdx, beta, asid, ainfo)
+		assert ret2 == hopFieldsNotConsDir(raw[:length], offset, currHFIdx, beta, asid, ainfo)
+		assert ret1 == ret2
+	}
+}
+
+ghost
+requires  0 < seg1Len
+requires  0 <= seg2Len
+requires  0 <= seg3Len
+requires  0 <= length && length <= len(raw)
+requires  pktLen(seg1Len, seg2Len, seg3Len) <= length
+requires  1 <= currINFIdx && currINFIdx < 4
+requires  (currINFIdx == 1 && seg2Len > 0) ==> len(asid) == seg2Len
+requires  (currINFIdx == 2 && seg2Len > 0 && seg3Len > 0) ==> len(asid) == seg3Len
+preserves acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R51)
+preserves acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R51)
+ensures   leftSeg(raw, currINFIdx, seg1Len, seg2Len, seg3Len, asid) ==
+	leftSeg(raw[:length], currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+decreases
+func leftSegWidenLemma(raw []byte, currINFIdx int, seg1Len int, seg2Len int, seg3Len int, asid seq[io.IO_as], length int) {
+	offset := hopFieldOffset(numInfoFields(seg1Len, seg2Len, seg3Len), 0)
+	if currINFIdx == 1 && seg2Len > 0 {
+		currSegWidenLemma(raw, offset + path.HopLen * seg1Len, currINFIdx, 0, asid, length)
+		ret1 := some(currSeg(raw, offset + path.HopLen * seg1Len, currINFIdx, 0, asid))
+		ret2 := some(currSeg(raw[:length], offset + path.HopLen * seg1Len, currINFIdx, 0, asid))
+		assert ret1 == reveal leftSeg(raw, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret2 == reveal leftSeg(raw[:length], currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret1 == ret2
+	} else if currINFIdx == 2 && seg2Len > 0 && seg3Len > 0 {
+		currSegWidenLemma(raw, offset + path.HopLen * (seg1Len + seg2Len), currINFIdx, 0, asid, length)
+		ret1 := some(currSeg(raw, offset + path.HopLen * (seg1Len + seg2Len), currINFIdx, 0, asid))
+		ret2 := some(currSeg(raw[:length], offset + path.HopLen * (seg1Len + seg2Len), currINFIdx, 0, asid))
+		assert ret1 == reveal leftSeg(raw, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret2 == reveal leftSeg(raw[:length], currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret1 == ret2
+	} else {
+		ret := none[io.IO_seg3]
+		assert ret == reveal leftSeg(raw, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret == reveal leftSeg(raw[:length], currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+	}
+}
+
+ghost
+requires  0 < seg1Len
+requires  0 <= seg2Len
+requires  0 <= seg3Len
+requires  0 <= length && length <= len(raw)
+requires  pktLen(seg1Len, seg2Len, seg3Len) <= length
+requires  -1 <= currINFIdx && currINFIdx < 2
+requires  (currINFIdx == 1 && seg2Len > 0 && seg3Len > 0) ==> len(asid) == seg2Len
+requires  (currINFIdx == 0 && seg2Len > 0) ==> len(asid) == seg1Len
+preserves acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R51)
+preserves acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R51)
+ensures   rightSeg(raw, currINFIdx, seg1Len, seg2Len, seg3Len, asid) ==
+	rightSeg(raw[:length], currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+decreases
+func rightSegWidenLemma(raw []byte, currINFIdx int, seg1Len int, seg2Len int, seg3Len int, asid seq[io.IO_as], length int) {
+	offset := hopFieldOffset(numInfoFields(seg1Len, seg2Len, seg3Len), 0)
+	if currINFIdx == 1 && seg2Len > 0 && seg3Len > 0 {
+		currSegWidenLemma(raw, offset + path.HopLen * seg1Len, currINFIdx, seg2Len, asid, length)
+		ret1 := some(currSeg(raw, offset + path.HopLen * seg1Len, currINFIdx, seg2Len, asid))
+		ret2 := some(currSeg(raw[:length], offset + path.HopLen * seg1Len, currINFIdx, seg2Len, asid))
+		assert ret1 == reveal rightSeg(raw, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret2 == reveal rightSeg(raw[:length], currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret1 == ret2
+	} else if currINFIdx == 0 && seg2Len > 0 {
+		currSegWidenLemma(raw, offset, currINFIdx, seg1Len, asid, length)
+		ret1 := some(currSeg(raw, offset, currINFIdx, seg1Len, asid))
+		ret2 := some(currSeg(raw[:length], offset, currINFIdx, seg1Len, asid))
+		assert ret1 == reveal rightSeg(raw, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret2 == reveal rightSeg(raw[:length], currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret1 == ret2
+	} else {
+		ret := none[io.IO_seg3]
+		assert ret == reveal rightSeg(raw, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret == reveal rightSeg(raw[:length], currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+	}
+}
+
+ghost
+requires  0 <= seg2Len
+requires  0 < seg1Len
+requires  0 <= length && length <= len(raw)
+requires  0 <= seg3Len
+requires  2 <= currINFIdx && currINFIdx < 5
+requires  pktLen(seg1Len, seg2Len, seg3Len) <= length
+requires  (currINFIdx == 2 && seg2Len > 0 && seg3Len > 0) ==> len(asid) == seg3Len
+requires  (currINFIdx == 4 && seg2Len > 0) ==> len(asid) == seg1Len
+preserves acc(sl.AbsSlice_Bytes(raw, 0, len(raw)), R51)
+preserves acc(sl.AbsSlice_Bytes(raw[:length], 0, len(raw[:length])), R51)
+ensures   midSeg(raw, currINFIdx, seg1Len, seg2Len, seg3Len, asid) ==
+	midSeg(raw[:length], currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+decreases
+func midSegWidenLemma(raw []byte, currINFIdx int, seg1Len int, seg2Len int, seg3Len int, asid seq[io.IO_as], length int) {
+	offset := hopFieldOffset(numInfoFields(seg1Len, seg2Len, seg3Len), 0)
+	if currINFIdx == 4 && seg2Len > 0 {
+		currSegWidenLemma(raw, offset, 0, seg1Len, asid, length)
+		ret1 := some(currSeg(raw, offset, 0, seg1Len, asid))
+		ret2 := some(currSeg(raw[:length], offset, 0, seg1Len, asid))
+		assert ret1 == reveal midSeg(raw, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret2 == reveal midSeg(raw[:length], currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret1 == ret2
+	} else if currINFIdx == 2 && seg2Len > 0 && seg3Len > 0 {
+		currSegWidenLemma(raw, offset + path.HopLen * (seg1Len + seg2Len), currINFIdx, 0, asid, length)
+		ret1 := some(currSeg(raw, offset + path.HopLen * (seg1Len + seg2Len), currINFIdx, 0, asid))
+		ret2 := some(currSeg(raw[:length], offset + path.HopLen * (seg1Len + seg2Len), currINFIdx, 0, asid))
+		assert ret1 == reveal midSeg(raw, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret2 == reveal midSeg(raw[:length], currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret1 == ret2
+	} else {
+		ret := none[io.IO_seg3]
+		assert ret == reveal midSeg(raw, currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+		assert ret == reveal midSeg(raw[:length], currINFIdx, seg1Len, seg2Len, seg3Len, asid)
+	}
+}
diff --git a/verification/io/io-spec.gobra b/verification/io/io-spec.gobra
index df46e6ae1..ef2fcb250 100644
--- a/verification/io/io-spec.gobra
+++ b/verification/io/io-spec.gobra
@@ -430,10 +430,4 @@ requires token(t) && CBio_IN_bio3s_exit(t, v)
 ensures  token(old(dp3s_iospec_bio3s_exit_T(t, v)))
 func Exit(ghost t Place, ghost v IO_val)
 
-ghost
-decreases
-requires token(t) && CBioIO_bio3s_send(t, v)
-ensures  token(old(dp3s_iospec_bio3s_send_T(t, v)))
-func Send(ghost t Place, ghost v IO_val)
-
-/** End of helper functions to perfrom BIO operations **/
\ No newline at end of file
+/** End of helper functions to perfrom BIO operations **/