@article{SF_1979__18_134364,
     author = {G. Lallement},
     title = {Some remarks on the four-spiral semigroup.},
     journal = {Semigroup forum},
     pages = {341--346},
     publisher = {mathdoc},
     volume = {18},
     year = {1979},
     zbl = {0428.20034},
     url = {http://geodesic.mathdoc.fr/item/SF_1979__18_134364/}
}