Dear Graham,
> On 12. Apr 2020, at 14:37, Ellis, Grahamj <graham.el...@nuigalway.ie> wrote:
>
> Dear GAP Community,
>
> Is there a way to construct a group homomorphism using a variant of the
> function
>
> f:=GroupHomomorphismByFunction(G,H,x->function(x))
Minor side remark: instead of writing
x->function(x)
you can just write
function
>
> for which
>
> ImageElm(f,x)
>
> does not test to see if x lies in G?
But ImageElm in the above setting never tests if x lies in G. It directly calls
the function you provided:
gap> f:=GroupHomomorphismByFunction(G,H,x->x^2);;
gap> Display(ApplicableMethod(ImageElm, [f, G.1]));
function ( map, elm )
return map!.fun( elm );
end
Any membership tests you are seeing must be caused by something else.
Cheers
Max
> Here function(x) is a well-defined function for x in G, but G is a group for
> which I don't have a membership test.
>
> Thanks,
>
> Graham
>
>
> School of Mathematics, Statistics & Applied Mathematics
> National University of Ireland, Galway
> tel: 091 493011
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