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Too general "Order" for automorphisms #3097

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@laurentbartholdi

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gap> f := FreeGroup(2);;
gap> x := GroupHomomorphismByImages(f,f,[f.1,f.2],[f.2,f.1]);;
gap> Order(x); # expects 2
Error, no method found! For debugging hints type ?Recovery from NoMethodFound
Error, no 3rd choice method found for `CompositionSeries' on 1 arguments at /usr/local/src/gap/lib/methsel2.g:250 called from
CompositionSeries( U ) at /usr/local/src/gap/lib/grpprmcs.gi:2690 called from
ChiefSeries( d ) at /usr/local/src/gap/lib/morpheus.gi:43 called from

the code in lib/morpheus.gi assumes that the source of the automorphism is a finite group. Presumably the method should give up when its source doesn't have the filter IsFinite.

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laurentbartholdi

laurentbartholdi commented on Dec 7, 2018

@laurentbartholdi
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In my example,

gap> ApplicableMethod(Order,[x],0,2)(x);
2
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added 3 commits that reference this issue on Dec 11, 2018
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added this to the GAP 4.11.0 milestone on Feb 15, 2020
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      Too general "Order" for automorphisms · Issue #3097 · gap-system/gap