[1] BIRKHOFF G.: Lattice theory. Am. Math. Soc. Coll. Publ. Vol. XXV, 3rd new ed., Providence RI, 1967. MR 0227053 | Zbl 0153.02501

[2] DILWORTH R. P.: The structure of relatively complemented lattices. Annals Math. 51 (1950), 348-359. MR 0033795 | Zbl 0036.01802

[3] MAEDA F.: Direct and subdirect factorization of lattices. J. Sci. Hiroshima Univ. Ser. A, 15 (1951-1952), 97-102. MR 0060475

[4] PAPERT D.: Congruence relations in semi-lattices. J. London Math. Soc. 39 (1964), 723-729. MR 0166123 | Zbl 0126.03802

[5] TANAKA T.: Canonical subdirect factorizations of lattices. J. Sci. Hiroshima Univ. Ser. A, 16 (1952-1953), 239-246. MR 0060476 | Zbl 0049.01704

[6] VARLET J.: Congruence dans les demi-lattis. Bull. Soc. Roy. Sei. Liège, 34 (1965), 231-240. MR 0182584

[7] NIEMINEN J.: About congruence relatione of semilattices. submitted to Acta Fac. Rer. Nat. Univ. Comen. Math.