@article{10_21136_CMJ_1971_101046,
     author = {Hall, Robert E.},
     title = {Commutative cancellative semigroups with two generators},
     journal = {Czechoslovak Mathematical Journal},
     pages = {449--452},
     year = {1971},
     volume = {21},
     number = {3},
     doi = {10.21136/CMJ.1971.101046},
     mrnumber = {0286920},
     zbl = {0244.20074},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1971.101046/}
}