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#W  ideals.gd
#Y  Copyright (C) 2013-15                                 James D. Mitchell
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##  Licensing information can be found in the README file of this package.
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DeclareSynonymAttr("GeneratorsOfSemigroupIdeal", GeneratorsOfMagmaIdeal);
DeclareGlobalFunction("SemigroupIdeal");

DeclareOperation("SemigroupIdealByGenerators",
                 [IsActingSemigroup,
                  IsAssociativeElementCollection,
                  IsRecord]);

DeclareAttribute("MinimalIdealGeneratingSet",
                 IsActingSemigroup and IsSemigroupIdeal);

# the <Parent> of an ideal is the semigroup in which the ideal was created,
# i.e.  the first argument of <SemigroupIdeal(S, I)>. The
# <SupersemigroupOfIdeal> is the object containing <GeneratorsOfSemigroup>
# which are used to compute the ideal. For a regular semigroup ideal,
# <SupersemigroupOfIdeal> will always be the top most semigroup used to create
# any of the predecessors of the current ideal. For example, if <S> is a
# semigroup, <I> is a regular ideal of <S>, and <J> is an ideal of <I>, then
# <Parent(J)> is <I> and <SupersemigroupOfIdeal(J)> is <S>.  This is to avoid
# computing a generating set for <I>, in this example, which is expensive and
# unnecessary since <I> is regular (in which case the Green's relations of <I>
# are just restrictions of the Green's relations on <S>).
#
# If <S> is a semigroup, <I> is a non-regular ideal of <S>, <J> is an ideal of
# <I>, then <SupersemigroupOfIdeal(J)> is <I>, since we anyway currently have
# to use a <GeneratorsOfSemigroup(I)> to compute anything about <I> other than
# its size and membership.

DeclareAttribute("SupersemigroupOfIdeal", IsSemigroupIdeal);

InstallTrueMethod(IsSemigroup, IsSemigroupIdeal);
