Narrow declarations of Factorization and WreathProduct

[james-d-mitchell]

This PR partially resolves:

gap-system/gap#6282

The part not resolved is that for StructureDescription, it seems that IsRcwaGroup and IsRcwaGroupOverZ imply IsGroupAsSemigroup (which make sense and is fine), but then the methods installed for StructureDescription for IsGroupAsSemigroup and something else (maybe IsGroup) collide. I'm not sure how to resolve this. Any suggestions @fingolfin ?

[fingolfin]

Alternatively we could also widen the declaration in GAP itself, which currently is

DeclareOperation( "Factorization",
                  [ IsGroup, IsMultiplicativeElementWithInverse ] );

The drawback of that would be that if GAP did that, loading any older Semigroups versions would produce a warning

#I  equal requirements in multiple declarations for operation `Factorization'

and the new semigroups would either only work on the new GAP; or would have to have code to the effect of "if GAp does not declare this operation for IsSemigroup then declare it for semigroups".

So I am not sure it would be worth that hassle.

[james-d-mitchell]

Agreed I'll just merge this for now (when updated) and then we can think about what to do later.

[fingolfin]

For StructureDescription my suggestion would be that you drop

DeclareAttribute("StructureDescription", IsGroupAsSemigroup);

and then change

InstallMethod(StructureDescription, "for a group as semigroup",

to

InstallOtherMethod(StructureDescription, "for a group as semigroup",

[james-d-mitchell]

For StructureDescription my suggestion would be that you drop

DeclareAttribute("StructureDescription", IsGroupAsSemigroup);

and then change

InstallMethod(StructureDescription, "for a group as semigroup",

to

InstallOtherMethod(StructureDescription, "for a group as semigroup",

Aha, right, I forgot about InstallOtherMethod, I'll do that. Thanks @fingolfin