@article{SF_1981__23_134500,
     author = {A. Varisco and A. Cherubini},
     title = {On conditionally commutative semigroups.},
     journal = {Semigroup forum},
     pages = {15--24},
     publisher = {mathdoc},
     volume = {23},
     year = {1981},
     zbl = {0471.20047},
     url = {http://geodesic.mathdoc.fr/item/SF_1981__23_134500/}
}