For a cancellative semigroup S and field F, it is proved that the algebra FS centrally essential if only group of fractions GS exists FGS essential. The has classical right ring which ring. There exist non-commutative algebras over fields zero characteristic (this contrasts with known fact are commutative).

It is well known that automatic groups can be characterized using geometric properties of their Cayley graphs. Along the same line of thought, we provide a geometric characterization of automatic monoids. This involves working with a slightly strengthened definition of an automatic monoid which is still a proper generalization of the concept of an automatic group. The two definitions coincide i...

An unital C∗-algebra A is said to have cancellation of projections if the semigroup D(A) of Murray-von Neumann equivalence classes of projections in matrices over A is cancellative. It has long been known that stable rank one implies cancellation for any A, and some partial converses have been established. In the sequel it is proved that cancellation does not imply stable rank one for simple, s...

In this paper, we characterize exactly the class of languages that are recognizable by nite loops, i.e. by cancellative binary algebras with an identity. This turns out to be the well-studied class of regular open languages. Our proof technique is interesting in itself: we generalize the operation of block product of monoids, which is so useful in the associative case, to the situation where th...

We introduce two partially overlapping classes of pathwise dualities between interacting particle systems that are based on commutative monoids (semigroups with a neutral element) and semirings, respectively. For whose local state space has elements, this approach yields unified treatment the well-known additive cancellative dualities. spaces three or more we discover several new