@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/