Abstract. A congruence of an algebra is called uniform if all the congruence classes are of the same size. An algebra is called uniform if each of its congruences is uniform. All algebras with a group reduct have this property. We prove that almost every finite uniform Mal'cev algebra with a congruence lattice of height at most two is polynomially equivalent to an expanded group.
MotivationIn this note, we investigate finite uniform algebras. We say that a congruence θ of an algebra A is uniform if all its congruence classes have the same cardinality. We say that an algebra A is uniform if all congruences of A are uniform. Uniform congruences have been introduced by W. Taylor in [13] and studied by R. McKenzie in [11]. In these papers, as in [4, p. 93], varieties of uniform algebras are considered rather than single uniform algebras. In 2005, K. Kaarli, [9], proved that finite uniform lattices are congruence permutable.Clearly, all algebras with a group reduct (groups, rings and modules as the most famous examples) are uniform. Similarly, all quasigroups are also uniform and therefore all algebras with a quasigroup reduct (expanded quasigroups) are uniform. Let us recall that a quasigroup is a groupoid (G, ·) such that for all a, b ∈ G there exist unique x and y in G such that ax = b and ya = b. Let a/θ and b/θ be two different classes of a congruence θ of the quasigroup G. We know that there is a c ∈ G such that a · c = b. We take the right translation f c : G → G, defined by f c (x) := x · c for all x ∈ G, and restrict it to a/θ. Then f c (a/θ) ⊆ b/θ because θ is compatible with · . Furthermore, f c is an injective mapping because · is a quasigroup operation. Hence, |a/θ| ≤ |b/θ|. Analogously, we obtain |b/θ| ≤ |a/θ|. If · has a neutral element in G, then we call (G, ·) a loop. An algebra A is called an expanded quasigroup (loop) if it has a quasigroup (loop) operation among its fundamental operations.Presented by E. Kiss.