[GAP Forum] Semigroup homomorphism

Jose Joao Morais jjoao at netcabo.pt
Thu Jan 22 18:33:59 GMT 2004

Dear GAP Forum,

	I am trying to define a semigroup homomorphism, so I looked at the code
for GroupGeneralMappingByImages in ghom.gi and tried to do something
similar for semigroups. This is what I did (poi5 is a semigroup of

gap> G:=poi5;
<monoid with 5 generators>
gap> H:=G;
<monoid with 5 generators>
gap> filter:=HasSource and HasRange and HasMappingGeneratorsImages;
<Operation "<<and-filter>>">
gap> gens:=GeneratorsOfSemigroup(G);;
gap> imgs:=GeneratorsOfSemigroup(H);;
gap> mapi:=[Immutable(gens),Immutable(imgs)];;
gap> hom:=rec();
rec(  )
gap> ObjectifyWithAttributes( hom,
>     NewType( GeneralMappingsFamily
>     ( ElementsFamily( FamilyObj( G ) ),
>       ElementsFamily( FamilyObj( H ) ) ), filter ),
>       Source,G,
>       Range,H,
>       MappingGeneratorsImages,mapi);
gap> SetIsMapping( hom, true );
gap> IsMapping(hom);
gap> Source(hom);
Error, no method found! For debugging hints type ?Recovery from
Error, no 1st choice method found for `Source' on 1 arguments called
<function>( <arguments> ) called from read-eval-loop
Entering break read-eval-print loop ...
you can 'quit;' to quit to outer loop, or
you can 'return;' to continue

	I could not find the code for  Source, so I would like to ask if
someone could tell me why this error happened or how can make this work.

	Thank you
	Jose Morais

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