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Merged
james-d-mitchell merged 3 commits into from
Mar 30, 2026
Merged

Narrow declarations of Factorization and WreathProduct #1156

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56dedad
Narrow declaration of Factorization
james-d-mitchell Mar 25, 2026
c9168f0
Narrow declaration of WreathProduct
james-d-mitchell Mar 25, 2026
e3d9c85
attr: don't declare StructureDescription for IsGroupAsSemigroup
james-d-mitchell Mar 30, 2026
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1 change: 0 additions & 1 deletion gap/attributes/attr.gd
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Original file line number Diff line number Diff line change
Expand Up @@ -53,7 +53,6 @@ DeclareAttribute("SmallestElementSemigroup", IsSemigroup);
DeclareAttribute("LargestElementSemigroup", IsSemigroup);

DeclareAttribute("StructureDescription", IsBrandtSemigroup);
DeclareAttribute("StructureDescription", IsGroupAsSemigroup);
DeclareAttribute("StructureDescriptionMaximalSubgroups",
IsSemigroup);
DeclareAttribute("MaximalDClasses", IsSemigroup);
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2 changes: 1 addition & 1 deletion gap/attributes/attr.gi
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Expand Up @@ -396,7 +396,7 @@ end);

# same method for ideals

InstallMethod(StructureDescription, "for a group as semigroup",
InstallOtherMethod(StructureDescription, "for a group as semigroup",
[IsGroupAsSemigroup],
function(S)
if IsGroup(S) then
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6 changes: 5 additions & 1 deletion gap/attributes/factor.gd
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Expand Up @@ -13,5 +13,9 @@ DeclareOperation("MinimalFactorization",
DeclareOperation("NonTrivialFactorization",
[IsSemigroup, IsMultiplicativeElement]);
DeclareOperation("Factorization", [IsLambdaOrb, IsPosInt, IsPerm]);
DeclareOperation("Factorization", [IsSemigroup, IsMultiplicativeElement]);

@fingolfin fingolfin Mar 27, 2026

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Alternatively we could also widen the declaration in GAP itself, which currently is

DeclareOperation( "Factorization",
                  [ IsGroup, IsMultiplicativeElementWithInverse ] );

The drawback of that would be that if GAP did that, loading any older Semigroups versions would produce a warning

#I  equal requirements in multiple declarations for operation `Factorization'

and the new semigroups would either only work on the new GAP; or would have to have code to the effect of "if GAp does not declare this operation for IsSemigroup then declare it for semigroups".

So I am not sure it would be worth that hassle.

@james-d-mitchell james-d-mitchell Mar 30, 2026

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Agreed I'll just merge this for now (when updated) and then we can think about what to do later.

DeclareOperation("Factorization",
[IsSemigroup and CanUseFroidurePin, IsMultiplicativeElement]);
DeclareOperation("Factorization",
[IsActingSemigroup and HasGeneratorsOfSemigroup,
IsMultiplicativeElement]);
DeclareOperation("TraceSchreierTreeForward", [IsSemigroupData, IsPosInt]);
5 changes: 5 additions & 0 deletions gap/semigroups/semifp.gd
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Expand Up @@ -26,3 +26,8 @@ DeclareOperation("ReversedOp", [IsElementOfFpMonoid]);

DeclareGlobalFunction("FreeMonoidAndAssignGeneratorVars");
DeclareGlobalFunction("FreeSemigroupAndAssignGeneratorVars");

DeclareOperation("Factorization", [IsFpSemigroup, IsElementOfFpSemigroup]);
DeclareOperation("Factorization", [IsFpMonoid, IsElementOfFpMonoid]);
DeclareOperation("Factorization", [IsFreeSemigroup, IsWord]);
DeclareOperation("Factorization", [IsFreeMonoid, IsWord]);
7 changes: 5 additions & 2 deletions gap/semigroups/semitrans.gd
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Expand Up @@ -42,8 +42,11 @@ DeclareOperation("EndomorphismMonoid", [IsDigraph, IsHomogeneousList]);
DeclareAttribute("DigraphCore", IsDigraph);

DeclareOperation("WreathProduct",
[IsMultiplicativeElementCollection,
IsMultiplicativeElementCollection]);
[IsTransformationMonoid, IsPermGroup]);
DeclareOperation("WreathProduct",
[IsPermGroup, IsTransformationSemigroup]);
DeclareOperation("WreathProduct",
[IsTransformationMonoid, IsTransformationSemigroup]);

DeclareAttribute("SmallestElementRClass", IsGreensRClass);
DeclareAttribute("LargestElementRClass", IsGreensRClass);
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