@article{03906763, title = {Constructions of positive commutative semigroups on the plane. II.}, journal = {International Journal of Mathematics and Mathematical Sciences}, volume = {8}, year = {1985}, pages = {321-324}, doi = {10.1155/S0161171285000333}, zbl = {0568.22003}, language = {en}, url = {http://dml.mathdoc.fr/item/03906763} }
Farley, Reuben W. Constructions of positive commutative semigroups on the plane. II.. International Journal of Mathematics and Mathematical Sciences, Tome 8 (1985) pp. 321-324. doi : 10.1155/S0161171285000333. http://gdmltest.u-ga.fr/item/03906763/