@article{SF_1992__44_1_135130,
     author = {D.A. Bredikhin},
     title = {Varieties  of groupoids associated  with involuted restrictive bisemigroups of binary relations.},
     journal = {Semigroup forum},
     pages = {87--92},
     year = {1992},
     volume = {44},
     number = {1},
     zbl = {0792.20066},
     url = {http://geodesic.mathdoc.fr/item/SF_1992__44_1_135130/}
}