Group coextensions were developed independently by Grillet  and Leech  for semigroups in general. They yield precise constructions of complete commutative semigroups in terms of abelian groups and group-free semigroups. This leads to the semigroup cohomology which is studied in the last chapters of this book.
KeywordsAbelian Group Minimal Element Commutative Semigroup Semi Group Ideal Extension
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