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avoid an attribute value after leaving a break loop #5731

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Oct 22, 2024
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avoid an attribute value after leaving a break loop #5731

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23 changes: 15 additions & 8 deletions lib/grpfp.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -260,14 +260,20 @@ BindGlobal( "MakeFpGroupCompMethod", function(CMP)
com:=x->Image(hom,x);
# if neither is known, try a faithful representation (forcing its
# computation)
elif FPFaithHom(fam)<>fail then
hom:=FPFaithHom(fam);
com:=x->Image(hom,x);
#T Here one could try more elaborate things first
# otherwise force computation of a normal form.
else
f:=FpElementNFFunction(fam);
com:=x->f(UnderlyingElement(x));
hom:= AttributeValueNotSet( FPFaithHom, fam );
if hom <> fail then
SetFPFaithHom( fam, hom );
com:=x->Image(hom,x);
#T Here one could try more elaborate things first
# otherwise force computation of a normal form.
else
f:=FpElementNFFunction(fam : CallFromMakeFpGroupCompMethod:= true);
com:=x->f(UnderlyingElement(x));
# Set the attribute value only *after* we are sure
# that the user has not interrupted the 'FpElementNFFunction' call.
SetFPFaithHom(fam, fail);
fi;
fi;
SetCanEasilyCompareElements(fam,true);
SetCanEasilySortElements(fam,true);
Expand Down Expand Up @@ -5185,7 +5191,8 @@ InstallMethod(FpElementNFFunction,true,[IsElementOfFpGroupFamily],0,
function(fam)
local iso,k,id,f,ran,g;
g:=CollectionsFamily(fam)!.wholeGroup;
if not (HasIsomorphismFpMonoid(g) and
if ValueOption( "CallFromMakeFpGroupCompMethod" ) <> true and
not (HasIsomorphismFpMonoid(g) and
HasReducedConfluentRewritingSystem(Image(IsomorphismFpMonoid(g)))) then
# first try whether the group is ``small''
iso:=FPFaithHom(fam);
Expand Down
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