Gusev, S. V.; Skokov, D.V.; Vernikov, B. M .
(ДЗ "Луганський національний університет імені Тараса Шевченка", 2018)
We completely determine all commutative semigroup varieties that are cancellable elements of the lattice SEM of all semigroup varieties. In particular, we verify that a commutative semigroup variety is a cancellable element ...