Let A and B be fields of subsets of a nonempty set X and let μ : A → E and ν : B → E be finitely additive measures (“charges”) taking values in a commutative semigroup E. We assume that μ and ν are consistent (e.g. μ = ν on A ∩ B) and ask whether they have a common extension to a charge ρ : A ∨ B → E. Now, we shall see (proposition 2.3) that the most natural consistency condition which we can f...

The set of residue classes, modulo any positive integer, is commutative and associative under the operation of multiplication. The author made the conjecture: For each finite commutative semigroup, S, there exists a positive integer, n, such that S is isomorphic with a subsemigroup of the multiplicative semigroup of residue classes (mod n). (A semigroup is a set closed with respect to a single-...

in the present paper, we consider biflatness of certain classes of semigroupalgebras. indeed, we give a necessary condition for a band semigroup algebra to bebiflat and show that this condition is not sufficient. also, for a certain class of inversesemigroups s, we show that the biflatness of ell^{1}(s)^{primeprime} is equivalent to the biprojectivity of ell^{1}(s).

The main purpose of this paper is to establish a relation between universality of certain P-compactifications of a semitopological semigroup and their corresponding enveloping semigroups. In particular, we show that if we take P to be the property that the enveloping semigroup of a compactification of a semitopological semigroup s is left simple, a group, or the trivial singleton semigroup, t...

The aim of this paper is to classify all monogenic ternary semigroups, up to isomorphism. We divide them to two groups: finite and infinite. We show that every infinite monogenic ternary semigroup is isomorphic to the ternary semigroup O, the odd positive integers with ordinary addition. Then we prove that all finite monogenic ternary semigroups with the same index...

Overlapping tile automata and the associated notion of recognizability by means of (adequate) premorphisms in finite ordered monoids have recently been defined for coping with the collapse of classical recognizability in inverse monoids. In this paper, we investigate more in depth the associated algebraic tools that allows for a better understanding of the underlying mathematical theory. In par...