@article{SF_1975__11_134133,
     author = {R.S. Pierce},
     title = {Arithmetic {Properties} of certain partially ordered {Semigeroups.}},
     journal = {Semigroup forum},
     pages = {115--129},
     publisher = {mathdoc},
     volume = {11},
     year = {1975},
     zbl = {0334.06006},
     url = {http://geodesic.mathdoc.fr/item/SF_1975__11_134133/}
}