1 Introduction
By an algebra G = (G, ., 0) we main a non-empty set G together with a binary
multiplication and a some distinguished element 0. In 1966, Y. Imai and K.
Iseki [2] defined a class of algebras of type (2,0) called BCK-algebra which
generalizes on one hand the notion of algebra of sets with the set subtraction
as the only fundamental non-nullary operation. on the other hand the notion
of implication algebra [1]. We can define an implication in each BCK- algebra
by y → x = xy. So, we can see (.) as the dual of implication of B-C-Klogic.
in this paper, a binary multiplication will be denoted by juxtaposition.
we use dots only to avoid repetitions of brackets. for example, the formula
((xy)(zy))(xz) = 0 will be written as (xy.zy).xz = 0.