@article{GDZPPN001263153, title = {Permutation functions and (n,m)-commutativity of semigroups .}, journal = {Semigroup forum}, volume = {48}, year = {1994}, pages = {71-78}, zbl = {0805.20051}, url = {http://dml.mathdoc.fr/item/GDZPPN001263153} }
Nagy, A. Permutation functions and (n,m)-commutativity of semigroups .. Semigroup forum, Tome 48 (1994) pp. 71-78. http://gdmltest.u-ga.fr/item/GDZPPN001263153/