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Fix FactorCosetAction(G, G) for perm. groups #5903

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merged 1 commit into from
Jan 11, 2025
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Fix FactorCosetAction(G, G) for perm. groups #5903

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4 changes: 3 additions & 1 deletion lib/csetperm.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -883,10 +883,12 @@
u:=G;
Error("only trivial operation ? I Set u:=G;");
fi;
if IsSubset(u, G) then
return DoFactorCosetAction(G, u, G);
fi;

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lib/csetperm.gi#L886-L888 

Added lines #L886 - L888 were not covered by tests
if N=false then
N:=Core(G,u);
fi;

ac:=ActionRefinedSeries(G,u);
actions:=ac[2];
ac:=ac[1];
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2 changes: 2 additions & 0 deletions lib/factgrp.gd
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Expand Up @@ -167,6 +167,8 @@ DeclareAttribute("NaturalHomomorphismsPool",IsGroup,
##
DeclareOperation( "FactorCosetAction", [IsGroup,IsGroup] );

DeclareGlobalFunction( "DoFactorCosetAction" );

#############################################################################
##
#F ImproveActionDegreeByBlocks( <G>, <N> , <hom> [,forceblocks] )
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2 changes: 1 addition & 1 deletion lib/factgrp.gi
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Expand Up @@ -475,7 +475,7 @@ end);
#F FactorCosetAction( <G>, <U>, [<N>] ) operation on the right cosets Ug
## with possibility to indicate kernel
##
BindGlobal("DoFactorCosetAction",function(arg)
InstallGlobalFunction("DoFactorCosetAction",function(arg)
local G,u,op,h,N,rt;
G:=arg[1];
u:=arg[2];
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2 changes: 2 additions & 0 deletions tst/teststandard/permgrp.tst
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Expand Up @@ -155,6 +155,8 @@ gap> u:=Normalizer(g,SylowSubgroup(g,3));;
gap> act:=FactorCosetAction(g,u);;
gap> NrMovedPoints(Range(act));
70840
gap> NrMovedPoints(Range(FactorCosetAction(g,g)));
0

#
gap> STOP_TEST("permgrp.tst");
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