@article{GDZPPN00125023X, title = {On the elementary theory of free inverse semigroups.}, journal = {Semigroup forum}, volume = {7}, year = {1974}, pages = {189-195}, zbl = {0299.20050}, url = {http://dml.mathdoc.fr/item/GDZPPN00125023X} }
Vazenin, Ju.M. On the elementary theory of free inverse semigroups.. Semigroup forum, Tome 7 (1974) pp. 189-195. http://gdmltest.u-ga.fr/item/GDZPPN00125023X/