@article{SF_1996__53_2_135466,
     author = {N.R. Reilly and S. Zhang},
     title = {Operators and products in the lattice of existence varieties of regular semigroups.},
     journal = {Semigroup forum},
     pages = {1--24},
     publisher = {mathdoc},
     volume = {53},
     number = {2},
     year = {1996},
     zbl = {0854.20069},
     url = {http://geodesic.mathdoc.fr/item/SF_1996__53_2_135466/}
}