A partial abelian semigroup (PAS) is a structure (L, Þ, ), where is a partial binary operation on L with domain Þ, 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 x, y L are perspective with respect to M, if there is z L such that x z M and y z M. 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.
IntroductionIn this paper, we will study some congruences on partial abelian semigroups, where a partial abelian semigroup is a structure (L, Þ, ), where is a partial binary operation on L with domain Þ, which is commutative and associative in a restricted sense ([37]). Similar structures have already appeared in the literature and found applications in several fields.A general theory of universal partial algebras can be found in [3]. A special case of partial groupoids -algebras with a partially defined binary operation -have been studied in [24].A common abstraction of Boolean rings and commutative lattice-ordered groups was introduced by Schmidt in 1985 [35]. In [36] such a not necessarily commutative partial semigroup structure is studied under the name minimal clan. A commutative minimal clan is a set E with a set S of pairs of summable elements of E, a partial addition +: S E, and an order relation 5 such that (E, S, +, 5) is a commutative lattice-ordered partial semigroup having the cancellative property Presented by R. W. Quackenbush. 1991 AMS Subject Classification: 06A06, 08A55, 06C15. Key words and phrases. Partial abelian semigroup, effect algebra, difference (operation) on a poset, orthomodular poset, orthoalgebra, difference poset, homomorphism and congruence of partial abelian semigroups, algebraic set.
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