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Merged
james-d-mitchell merged 1 commit into from
May 1, 2026
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Tests for AsSemigroup with 4 arguments #927

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4 changes: 2 additions & 2 deletions gap/digraph.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -1314,11 +1314,11 @@ function(filt, digraph, gps, homs)
fi;
od;

reps := [];
reps := EmptyPlist(n);
for i in [1 .. n] do
rep := IsomorphismPermGroup(gps[i]);
rep := rep * SmallerDegreePermutationRepresentation(Image(rep));
Add(reps, rep);
reps[i] := rep;
od;

top := DigraphTopologicalSort(digraph);
Expand Down
26 changes: 22 additions & 4 deletions tst/standard/digraph.tst
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Original file line number Diff line number Diff line change
Expand Up @@ -13,11 +13,11 @@
#@local adjacencies, b, bin, c, c1, c2, d, di, digraph, divides, elms, eq
#@local eq_distr, eq_new, error, f, failed, failed_names, failed_values, foo, g
#@local gr, gr1, gr2, gr3, gr4, gr5, graph, graph1, graph2, grnc, group, h
#@local hom13, hom21, hom23, hom31, hom41, hom42, hom52, hom53, i, im, inn
#@local isGraph, iso, iso_distr, iso_new, j, k, list, m, main, mat, n, name
#@local hom13, hom21, hom23, hom31, hom41, hom42, hom52, hom53, i, idhom, im
#@local inn, isGraph, iso, iso_distr, iso_new, j, k, list, m, main, mat, n, name
#@local name2, names, new, order, p, prop, properties, r, r1, r2, record, rel1
#@local rel2, rel3, representatives, s, schreierVector, sgn, temp, test, v, x
#@local xxx, y
#@local rel2, rel3, representatives, s, schreierVector, sgn, swaphom, temp
#@local test, v, x, xxx, y
gap> START_TEST("Digraphs package: standard/digraph.tst");
gap> LoadPackage("digraphs", false);;

Expand Down Expand Up @@ -1515,6 +1515,9 @@ Error, no 2nd choice method found for `AsSemigroup' on 2 arguments
gap> S := AsMonoid(IsTransformation, di);;
Error, the 1st argument <filt> must be IsPartialPermMonoid or IsPartialPermSem\
igroup,
gap> AsSemigroup(IsTransformationSemigroup, ChainDigraph(3), [], []);
Error, no method found! For debugging hints type ?Recovery from NoMethodFound
Error, no 2nd choice method found for `AsSemigroup' on 4 arguments

# AsSemigroup (for IsPartialPermSemigroup, a digraph, a list of groups,
# and homomorphisms)
Expand Down Expand Up @@ -1578,6 +1581,9 @@ gap> Size(T);
24
gap> Size(GreensHClassOfElement(T, Representative(T)));
24
gap> T := AsSemigroup(IsPartialPermSemigroup, gr3, [Group(())], []);;
gap> Size(T);
1
gap> gr4 := Digraph([[1], [1, 2], [1, 3], [1, 4], [1, 2, 3, 5]]);;
gap> G5 := AlternatingGroup(4);;
gap> G2 := SymmetricGroup(4);;
Expand Down Expand Up @@ -1671,6 +1677,18 @@ gap> T := AsSemigroup(IsPartialPermSemigroup, gr4, [G1, G2, G3, G4, G5],
> [[2, 1, hom21], [3, 1, hom31], [4, 1, hom41], [5, 2, hom52], [5, 2, hom52]]);;
Error, the fourth argument must contain a triple [i, j, hom] for each edge [i,\
j] in the reflexive transitive reduction of the second argument,
gap> D := Digraph([[1, 2, 3, 4], [2, 4], [3, 4], [4]]);;
gap> OutNeighbours(DigraphReflexiveTransitiveReduction(D));
[ [ 2, 3 ], [ 4 ], [ 4 ], [ ] ]
gap> G := SymmetricGroup(4);;
gap> idhom := GroupHomomorphismByFunction(G, G, IdFunc);;
gap> swaphom := GroupHomomorphismByFunction(G, G, x -> x ^ (1, 2));;
gap> T := AsSemigroup(IsPartialPermSemigroup, D, [G, G, G, G],
> [[1, 2, idhom], [1, 3, swaphom], [2, 4, idhom], [3, 4, swaphom]]);
<partial perm semigroup of rank 16 with 8 generators>
gap> T := AsSemigroup(IsPartialPermSemigroup, D, [G, G, G, G],
> [[1, 2, idhom], [1, 3, swaphom], [2, 4, idhom], [3, 4, idhom]]);
Error, the homomorphisms given must form a commutative diagram,

# MakeImmutable
gap> D := NullDigraph(IsMutableDigraph, 10);
Expand Down
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