@article{10_1017_S0017089507003448,
     author = {K\'ATAI-URB\'AN, KAMILLA and SZAB\'O, CSABA},
     title = {ON {THE} {FREE} {SPECTRUM} {OF} {THE} {VARIETY} {GENERATED} {BY} {THE} {COMBINATORIAL} {COMPLETELY} {0-SIMPLE} {SEMIGROUPS}},
     journal = {Glasgow mathematical journal},
     pages = {93--98},
     year = {2007},
     volume = {49},
     number = {1},
     doi = {10.1017/S0017089507003448},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089507003448/}
}