@article{SF_1977__14_186378,
     author = {J. A. Gerhard},
     title = {Semigroups with idempotent powers, {II:} {The} lattices of equational subclasses of  [(xy2 =xy] .},
     journal = {Semigroup forum},
     pages = {375--388},
     publisher = {mathdoc},
     volume = {14},
     year = {1977},
     zbl = {0373.20052},
     url = {http://geodesic.mathdoc.fr/item/SF_1977__14_186378/}
}