@article{GDZPPN001253182, title = {A theorem on binary relations and infinite languages.}, journal = {Semigroup forum}, volume = {18}, year = {1979}, pages = {307-316}, zbl = {0425.20053}, url = {http://dml.mathdoc.fr/item/GDZPPN001253182} }
Schwarz, Stefan. A theorem on binary relations and infinite languages.. Semigroup forum, Tome 18 (1979) pp. 307-316. http://gdmltest.u-ga.fr/item/GDZPPN001253182/