Congruences in partial abelian semigroups

A partial abelian semigroup (PAS) is a structure , where is a partial binary operation on L with domain , which is commutative and associative (whenever the corresponding elements exist). A class of congruences on partial abelian semigroups are studied such that the corresponding quotient is again a PAS. If M is a subset of a PAS L, we say that are perspective with respect to M, if there is such that and A subset M is called weakly algebraic if perspectivity with respect to M is a congruence. Some conditions are shown under which a congruence coincides with a perspectivity with respect to an appropriate set M. Especially, conditions under which the corresponding quotient is a D-poset are found. It is also shown that every congruence of MV-algebras and orthomodular lattices is given by a perspectivity with respect to an appropriate set M. Received July 17, 1995; accepted in final form September 16, 1996.