Geodesic
The Lattice of Equational Classes of Commutative Semigroups
Canadian journal of mathematics, Tome 23 (1971) no. 5, pp. 875-895

Voir la notice de l'article provenant de la source Cambridge University Press

There has been some interest lately in equational classes of commutative semigroups (see, for example, [2; 4; 7; 8]). The atoms of the lattice of equational classes of commutative semigroups have been known for some time [5]. Perkins [6] has shown that each equational class of commutative semigroups is finitely based. Recently, Schwabauer [7; 8] proved that the lattice is not modular, and described a distributive sublattice of the lattice.The present paper describes a “skeleton” sublattice of the lattice, which is isomorphic to A × N + with a unit adjoined, where A is the lattice of pairs (r, s) of non-negative integers with r ≦ s and s ≧ 1, ordered component-wise, and N + is the natural numbers with division. 
Nelson, Evelyn. The Lattice of Equational Classes of Commutative Semigroups. Canadian journal of mathematics, Tome 23 (1971) no. 5, pp. 875-895. doi: 10.4153/CJM-1971-098-0
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