possible bug in FiningStabiliser

[Jan De Beule]

Patrick Maier contacted me describing a possible bug in FiningStabiliser. He sent a piece of code that easily demonstrates the problem. In this piece of code, version numbers are mentioned. The problem is still there with GAP4.8.8, fining 1.4, orb 4.7.6, genss 1.6.4 and cvec 2.5.7. The problem is caused by lines -5 and -6 (commented out in this piece)

## Patrick Maier, 10 Apr 2017
##
## FiningStabiliser bug?
##
## Uncommenting the definitions of g12345a or g12345b below appears to
## cause non-termination.
##
## Versions:
## GAP 4.8.6
## FinInG 1.3.3
## Forms 1.2.3
## orb 4.7.6
## cvec 2.5.6
## genss 1.6.4
## GRAPE 4.7

LoadPackage("fining");

ps := PG(2, 9);   ## broken
#ps := PG(2, 8);   ## works
#ps := PG(2, 11);  ## works

as := AsSet(Points(ps));

g0 := CollineationGroup(ps);
Size(g0);

g1 := FiningSetwiseStabiliser(g0, as{[1]});
Size(g1);

g12 := FiningSetwiseStabiliser(g0, as{[1..2]});
Size(g12);

g123 := FiningSetwiseStabiliser(g0, as{[1..3]});
Size(g123);

g1234 := FiningSetwiseStabiliser(g0, as{[1..4]});
Size(g1234);

#g12345a := FiningSetwiseStabiliser(g0, as{[1..5]});   ## appears to diverge
#g12345b := FiningStabiliser(g1234, as[5]);            ## appears to diverge
g12345c := FiningStabiliserOrb(g1234, as[5]);         ## works
g12345d := Stabilizer(g1234, as[5], OnProjSubspaces); ## works

g12345c = g12345d;
Size(g12345c);