@article{SF_1971__3_133845,
     author = {M.S. Putcha and J. Weissglass},
     title = {Semigroups satisfying variable identities.},
     journal = {Semigroup forum},
     pages = {64--67},
     publisher = {mathdoc},
     volume = {3},
     year = {1971},
     zbl = {0235.20055},
     url = {http://geodesic.mathdoc.fr/item/SF_1971__3_133845/}
}