Laurent Bartholdi wrote:
> Hello world,
> Unless I'm terribly mistaken there's a problem with the FGA package:
>
> GAP4, Version: 4.4.6 of 02-Sep-2005, i686-pc-linux-gnu-gcc
> gap> RequirePackage("FGA");
> true
> gap> F := FreeGroup(2);
> <free group on the generators [ f1, f2 ]>
> ### the identity automorphism
> gap> x :=
> GroupHomomorphismByImages(F,F,GeneratorsOfGroup(F),GeneratorsOfGroup(F));
> [ f1, f2 ] -> [ f1, f2 ]
> gap> IsOne(x);
> ### and GAP freezes.
GAP uses a very general method which does not work for infinite groups,
and the FGA package implements no special method.
You can use this one:
InstallMethod( IsOne,
"for group general mappings with images",
[ IsGroupHomomorphism and HasMappingGeneratorsImages ],
hom -> IsEndoMapping( hom ) and MappingGeneratorsImages( hom )[ 1 ] =
MappingGeneratorsImages( hom )[ 2 ]
);
(As a workaround, you may prefer x=IdentityMapping(F).)
To the developers:
I guess something like the above method should go somewhere to the
gap library as it is not free group specific.
All the best
Christian Sievers
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