@article{GDZPPN002486504,
title = {Functions with a Finite Number of Negative Squares on Semigroups.},
journal = {Monatshefte f\"ur Mathematik},
volume = {108},
year = {1989},
pages = {9-34},
zbl = {0671.43008},
url = {http://dml.mathdoc.fr/item/GDZPPN002486504}
}
Berg, Christian; Sasvári, Zoltán. Functions with a Finite Number of Negative Squares on Semigroups.. Monatshefte für Mathematik, Tome 108 (1989) pp. 9-34. http://gdmltest.u-ga.fr/item/GDZPPN002486504/