Principal congruence relations and principal tolerances on varieties of lattices Jaromír Duda (1989) Mathematica Slovaca Similarity:
Algebras whose principal congruences form a sublattice of the congruence lattice Ivan Chajda (1988) Czechoslovak Mathematical Journal Similarity:
Varieties having distributive lattices of quasiorders Ivan Chajda (1991) Czechoslovak Mathematical Journal Similarity: