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@article{SF_1977__14_186363, author = {E. V. Sukhanov}, title = {The groupoid of varieties of idempotent semigroups.}, journal = {Semigroup forum}, pages = {143--160}, publisher = {mathdoc}, volume = {14}, year = {1977}, zbl = {0366.20043}, url = {http://geodesic.mathdoc.fr/item/SF_1977__14_186363/} }
E. V. Sukhanov. The groupoid of varieties of idempotent semigroups.. Semigroup forum, Tome 14 (1977), pp. 143-160. http://geodesic.mathdoc.fr/item/SF_1977__14_186363/