@article{10_4153_CJM_1996_045_3,
     author = {Popescu, Gelu},
     title = {Positive-Defininte {Functions} on {Free} {Semigroups}},
     journal = {Canadian journal of mathematics},
     pages = {887--896},
     year = {1996},
     volume = {48},
     number = {4},
     doi = {10.4153/CJM-1996-045-3},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1996-045-3/}
}