@article{SF_1992__45_3_135193,
     author = {D. Cowan},
     title = {An associative operator  on the lattice of varieties of inverse semigroups.},
     journal = {Semigroup forum},
     pages = {288--301},
     publisher = {mathdoc},
     volume = {45},
     number = {3},
     year = {1992},
     zbl = {0782.20050},
     url = {http://geodesic.mathdoc.fr/item/SF_1992__45_3_135193/}
}