@article{SF_1974__8_134023,
     author = {F.R. McMorris and C.S. jr. Johnson},
     title = {Semigroups for which every {S-system} has the natural partial order.},
     journal = {Semigroup forum},
     pages = {51--55},
     publisher = {mathdoc},
     volume = {8},
     year = {1974},
     zbl = {0284.20064},
     url = {http://geodesic.mathdoc.fr/item/SF_1974__8_134023/}
}