@article{SF_1993__46_1_135231,
     author = {J. Jezek and R. McKenzie},
     title = {Definability in the lattice of equational  theories of semigroups.},
     journal = {Semigroup forum},
     pages = {199--245},
     publisher = {mathdoc},
     volume = {46},
     number = {1},
     year = {1993},
     zbl = {0782.20051},
     url = {http://geodesic.mathdoc.fr/item/SF_1993__46_1_135231/}
}