@article{MAN_1976__223_162890,
     author = {Christian Berg and Christensen, Jens Peter Reus Christensen and Paul Ressel},
     title = {Positive {Definite} {Functions} on {Abelian} {Semigroups.}},
     journal = {Mathematische Annalen},
     pages = {253--274},
     publisher = {mathdoc},
     volume = {223},
     year = {1976},
     zbl = {0331.43010},
     url = {http://geodesic.mathdoc.fr/item/MAN_1976__223_162890/}
}