@article{MOMA_1989__107_3_178410,
     author = {Christian Berg and Zolt\'an Sasv\'ari},
     title = {Functions with a {Finite} {Number} of {Negative} {Squares} on {Semigroups.}},
     journal = {Monatshefte f\"ur Mathematik},
     pages = {9--34},
     publisher = {mathdoc},
     volume = {107},
     number = {3},
     year = {1989},
     zbl = {0671.43008},
     url = {http://geodesic.mathdoc.fr/item/MOMA_1989__107_3_178410/}
}