IsSubset for Integers and a long range hangs

[Stefan-Kohl]

Observed behaviour (GAP 4.15.1):

gap> IsSubset(Integers,[1..10^15]);
(... hangs ... )

Expected behaviour:

gap> IsSubset(Integers,[1..10^15]);
true

[james-d-mitchell]

Looks like the method that applies is (from coll.gi lines 2296 to 2303):

InstallMethod( IsSubset,
    "for two collections (loop over the elements of the second)",
    IsIdenticalObj,
    [ IsCollection,
      IsCollection ],
function( D, E )
    return ForAll( E, e -> e in D );
end );

This could probably be resolved by adding a special method such as:

InstallMethod( IsSubset,
    "for Integers and range",
    IsIdenticalObj,
    [ IsIntegers,
      IsRangeRep ],
ReturnTrue );

(not tested), perhaps there's a more general version of this that is more widely applicable?

[fingolfin]

Rationals, Integers, PositiveIntegers, GaussianIntegers etc. are all bespoke objects. One indeed needs to add special case methods for them, and there is potentially a lot (e.g. you might want to have a fast Union(Integers, [1..4]) or Union(Integers, Rationals), or ... Though I'd wonder: why?!

That said, if someone (e.g. @Stefan-Kohl ?) would like to submit PRs to add such methods, I'd be happy to review and merge them.