Abstract. A general construction of the free algebra over a poset in varieties finitely generated is given in [8]. In this paper, we apply this to the varieties of Łukasiewicz-Moisil algebras, giving a detailed description of the free algebra over a finite poset pX, ≤q, Free n ppX, ≤qq. As a consequence of this description, the cardinality of Free n ppX, ≤qq is computed for special posets.
IntroductionIn 1945, R. Dilworth ([5]) introduced the notion of free lattice over a poset. Later, this notion was adapted to different classes of algebras that arise from non-classical logics, these classes constitute varieties of algebras, which have an underlying order structure definable by means of certain equations p i px, yq " q i px, yq, 1 ≤ i ≤ n, in terms of the algebra's operations and some positive integer n. Constructions of this particular free algebra have been exhibited for different kinds of algebras such as bounded distributive lattices, De Morgan algebras and Hilbert algebras (see [7,8]).Consider, now, the set Ω of operations of type τ and the set E of identities. We shall note Alg tΩ,E,≤u , the category whose objects are tΩ, Eu-algebras, which have an order structure definable from the operations of Ω and the arrows are the respective tΩ, Eu-morphisms.The notion of free algebra over a poset relative to Alg tΩ,E,≤u can be defined as follows: Definition 1. Let pX, ≤q " X ≤ be a poset. We shall say that Free Alg tΩ,E,≤u pX ≤ q is the free algebra over pX, ≤q if the following conditions are satisfied:2010 Mathematics Subject Classification: 08B20, 03C05, 03G25. Key words and phrases: algebras, free algebras over a poset, Łukasiewicz-Moisil algebras.