make IsDualSemigroupRep not a representation

doc/dual.xml

@@ -96,15 +96,17 @@ false]]></Example> </Description> </ManSection>
 <#GAPDoc Label="IsDualSemigroupRep">
  <ManSection>
  <Filt Name = "IsDualSemigroupRep" Type = "Category" Arg="sgrp"/>
- <Returns>Returns <K>true</K> if <A>sgrp</A> is represented as
- a dual semigroup.</Returns>
+ <Returns>Returns <K>true</K> if <A>sgrp</A> lies in the category of
+ dual semigroups.</Returns>
  <Description>
  Semigroups created using <Ref Func="DualSemigroup"/>
- normally have this representation. The exception is semigroups
+ normally lie in this category. The exception is semigroups
  which are the dual of semigroups already lying in this category.
- That is, a semigroup has the representation
+ That is, a semigroup lies in the category
  <Ref Filt="IsDualSemigroupRep"/> if and only if the corresponding
- dual semigroup does not.
+ dual semigroup does not. Note that this is not a Representation in the
+ GAP sense, and will likely be renamed in a future major release of the
+ package.
 <Example>
 <![CDATA[
 gap> S := Semigroup([Transformation([3, 5, 1, 1, 2]),

gap/attributes/dual.gd

@@ -13,11 +13,9 @@ DeclareCategory("IsDualSemigroupElement", IsAssociativeElement);
 DeclareCategoryCollections("IsDualSemigroupElement");
 DeclareAttribute("DualSemigroup", IsSemigroup);
 
-# Every semigroup is mathematically a dual semigroup
-# What we care about is whether it is represented as one
-DeclareRepresentation("IsDualSemigroupRep",
- IsDualSemigroupElementCollection and IsSemigroup,
- []);
+# TODO (major release): remove "Rep" and update docs
+DeclareCategory("IsDualSemigroupRep",
+ IsDualSemigroupElementCollection and IsSemigroup);
 
 DeclareAttribute("DualSemigroupOfFamily", IsFamily);
 DeclareAttribute("AntiIsomorphismDualSemigroup", IsSemigroup);