[1] Beutler E.: An idealtheoretic characterization of varieties of abelian $\Omega$-groups. Algebra Univ. 8 (1978), 91-100. DOI 10.1007/BF02485374 | MR 0450169

[2] Csákány B.: Characterizations of regular varieties. Acta Sci. Math. (Szeged) 31 (1970), 187-189. MR 0272697

[3] Day A.: A characterization of modularity for congruence lattices of algebras. Canad. Math. Bull. 12 (1969), 167-173. DOI 10.4153/CMB-1969-016-6 | MR 0248063

[4] Duda J.: On two schemes applied to Маl'cev type theorems. Ann. Univ. Sci. Budapest, Sectio Math. 26 (1983), 39-45. MR 0719774

[5] Geigher D.: Coherent algebras. Notices AMS 21 (1974), A-436.

[6] Grätzer G.: Universal Algebra. 2nd expanded ed., Springer-Verlag, Berlin-Heidelberg-New York 1979. MR 0538623

[7] Gumm H.-P., Ursini A.: Ideals in universal algebras. Algebra Univ. 19 (1984), 45-54. DOI 10.1007/BF01191491 | MR 0748908 | Zbl 0547.08001

[8] Hagemann J., Mitschke A.: On n-permutable congruences. Algebra Univ. 3 (1973), 8-12. DOI 10.1007/BF02945100 | MR 0330010 | Zbl 0273.08001

[9] Mal'cev A. I.: On the general theory of algebraic systems. (Russian). Mat. Sbornik (New Series) 35 (77), (1954), 3-20. MR 0065533

[10] Werner H., Wille R.: Über den projektiven Abschluss von Äquivalenzklassengeometrien. Beiträge zur geometrischen Algebra. 345-352, Birkhäuser Verlag, Basel 1977. MR 0552769