GeneratorsOfSemigroup for a RZMS ideal

Originally reported by: wilfwilson (Bitbucket: wilfwilson, GitHub: wilfwilson)

GeneratorsOfSemigroup is failing when trying to compute the generators of a particular RZMS ideal inside MaximalSubsemigroups:

#!gap

gap> G:=Group([ (1,2,3,4), (1,3,2,4) ]);;
gap> mat2:=[ [ (), (3,4), 0 ], [ (1,3)(2,4), 0, 0 ], [ 0, 0, (3,4) ] ];;
gap> r2:=ReesZeroMatrixSemigroup(G,mat2);
<Rees 0-matrix semigroup 3x3 over Group([ (1,2,3,4), (1,3,2,4) ])>
gap> max:=Filtered(MaximalSubsemigroups(r2),IsActingSemigroup);;
gap> T:=max[30];
<subsemigroup of 3x3 Rees 0-matrix semigroup with 14 generators>
gap> MaximalSubsemigroups(T);
#I  finding irredundant generating set...
at  14 of   14 with     6 redundant,    5 non-redundant
#I  finding D-classes of generators...
#I  finding maximal subsemigroups arising from maximal D-classes...
#I  considering D-class 1
#I  calculating the ideal S minus D
Error, List Element: <list> must be a list (not a boolean) in
  return Objectify( TypeReesMatrixSemigroupElements( s ), 
   [ i, mat[j][i] ^ -1, j, mat ] ); called from 
IdempotentCreator( s )( o[i], rho ) called from
GroupHClass( d ) called from
InjectionPrincipalFactor( D[i] ) called from
SemigroupData( I ) called from
GeneratorsOfSemigroup( V ) called from
...  at line 47 of *stdin*
you can replace <list> via 'return <list>;'
brk>

Hopefully if you run this you'll get to the same spot. I'm still in the ideals branch. To give some slightly further information:

#!gap

brk> V;
<non-regular Rees 0-matrix semigroup ideal with 5 generators>
brk> GeneratorsOfSemigroupIdeal(V);
[ (1,(),3), (1,(1,4,3,2),2), (3,(),2), (2,(),2), 0 ]

i.e. V:=SemigroupIdeal(T, the above gens);

That aside, MaximalSubsemigroups seems to be working pretty well for acting subsemigroups RZMSs, that i've tried so far.

Bitbucket: https://bitbucket.org/james-d-mitchell/semigroups/issue/84

semigroups / Semigroups

GeneratorsOfSemigroup for a RZMS ideal #81