@article{SF_1977__14_186373,
     author = {T. E. Hays},
     title = {...- semigroups.},
     journal = {Semigroup forum},
     pages = {277--282},
     publisher = {mathdoc},
     volume = {14},
     year = {1977},
     zbl = {0387.22002},
     url = {http://geodesic.mathdoc.fr/item/SF_1977__14_186373/}
}