On combinatorial inverse semigroups
Paolo Aglianò · Use Siena air (University of Siena) · 1992
A characterization of all the simple (in the universal algebraci sense) combinatorial inverse semigroups, as well as of the monolith of the subdirectly irreducible ones, is obtained. Then the ideal of varieties of combinatorial inverse semigroups is studied and a theorem is proved, which states that the variety of semilattices has a unique upper cover.