Hyperassociative varieties of semigroups.
M-Solid Subvarieties of some Varieties of Commutative Semigroups
∗ The research of the author was supported by the Alexander v. Humboldt-Stiftung. The basic concepts are M -hyperidentities, where M is a monoid of hypersubstitutions. The set of all M -solid varieties of semigroups forms a complete sublattice of the lattice of all varieties of semigroups. We fix some specific varieties V of commutative semigroups and study the set of all M -solid subvarieties of V , in particular, if V is nilpotent.
Free systems of algebras and ultraclosed classes.
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