@article{SF_1971__3_133846,
     author = {M.S. Putcha and A. Yaqub},
     title = {Semigroups satisfying permutation identities.},
     journal = {Semigroup forum},
     pages = {68--73},
     publisher = {mathdoc},
     volume = {3},
     year = {1971},
     zbl = {0235.20059},
     url = {http://geodesic.mathdoc.fr/item/SF_1971__3_133846/}
}