[1] Barbour G. D., Raftery J. G.: On the degrees of permutаbility of subregulаr vаrieties. preprint 1994.
[2] Chajda I.:
Regulаrity аnd permutаbility of congruences. Algebra Univ. 11 (1980), 159-162.
MR 0588209
[3] Duda J.:
Mаľcev condition for regulаr аnd weаkly regulаr subаlgebrаs of the squаre. Acta Sci. Math. (Szeged) 46 (1983), 29-34.
MR 0739019
[4] Duda J.:
Mаľcev conditions for subаlgebrаs аlgebrаs. Acta Sci. Math. (Szeged) 51 (1987), 329-334.
MR 0940937