Geodesic
Examples of varieties of semigroups
Matematičeskie zametki, Tome 3 (1968) no. 6, pp. 663-670 
V. L. Murskii. Examples of varieties of semigroups. Matematičeskie zametki, Tome 3 (1968) no. 6, pp. 663-670. http://geodesic.mathdoc.fr/item/MZM_1968_3_6_a5/
@article{MZM_1968_3_6_a5,
     author = {V. L. Murskii},
     title = {Examples of varieties of semigroups},
     journal = {Matemati\v{c}eskie zametki},
     pages = {663--670},
     year = {1968},
     volume = {3},
     number = {6},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1968_3_6_a5/}
}
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Voir la notice de l'article provenant de la source Math-Net.Ru

An example of a variety $\mathfrak M$ of semigroups is formulated, where $\mathfrak M$ is defined by a finite number of identity relations for which the set of all identities (here strictly in two variables $x$, $y$) that hold on all semigroups of $\mathfrak M$ is nonrecursive. It is shown how to formulate similar varieties of semigroups with 1.