@article{GDZPPN001259954, title = {On spectra of solvability and attainability for varieties of semigroups.}, journal = {Semigroup forum}, volume = {38}, year = {1989}, pages = {129-156}, zbl = {0679.20053}, url = {http://dml.mathdoc.fr/item/GDZPPN001259954} }
Martynov, L.M. On spectra of solvability and attainability for varieties of semigroups.. Semigroup forum, Tome 38 (1989) pp. 129-156. http://gdmltest.u-ga.fr/item/GDZPPN001259954/