Incorrect result in IsFactorisableInverseMonoid for an ideal

[wilfwilson]

I and J are equal, but one is a factorisable inverse monoid, and the other is not:

gap> S := SymmetricInverseMonoid(5);;
gap> I := MinimalIdeal(S);;
gap> IsFactorisableInverseMonoid(I);
false
gap> J := InverseMonoid(I);;
gap> I = J;
true
gap> IsFactorisableInverseMonoid(J);
true

[james-d-mitchell]

Yikes, thanks for the report @wilfwilson!

[james-d-mitchell]

For info the old method for IsFactorisableInverseMonoid for an ideal is:

InstallMethod(IsFactorisableInverseMonoid, "for an inverse semigroup ideal",
[IsSemigroupIdeal and IsInverseSemigroup],
function(I)
  if I = SupersemigroupOfIdeal(I) then
    return IsFactorisableInverseMonoid(SupersemigroupOfIdeal(I));
  fi;
  return false;
end);

This is clearly incorrect, as your example shows. A fix is in the works.

[james-d-mitchell]

Fixed by PR #539

[james-d-mitchell]

Resolved in v3.0.20.