@article{GDZPPN001259539, title = {Expletives in languages and middle units in semigroups.}, journal = {Semigroup forum}, volume = {38}, year = {1989}, pages = {77-84}, zbl = {0662.20043}, url = {http://dml.mathdoc.fr/item/GDZPPN001259539} }
Tully, Edward J. Expletives in languages and middle units in semigroups.. Semigroup forum, Tome 38 (1989) pp. 77-84. http://gdmltest.u-ga.fr/item/GDZPPN001259539/