General mutants in semigroups.
A semigroup is called a generalized -semigroup if there exists a group congruence on such that the identity class contains a greatest element with respect to the natural partial order of . Using the concept of an anticone, all partially ordered groups which are epimorphic images of a semigroup are determined. It is shown that a semigroup is a generalized -semigroup if and only if contains an anticone, which is a principal order ideal of . Also a characterization by means of the structure...
An inflation of an algebra is formed by adding a set of new elements to each element in the original or base algebra, with the stipulation that in forming products each new element behaves exactly like the element in the base algebra to which it is attached. Clarke and Monzo have defined the generalized inflation of a semigroup, in which a set of new elements is again added to each base element, but where the new elements are allowed to act like different elements of the base, depending on the context...
We prove that any countable set of surjective functions on an infinite set of cardinality ℵₙ with n ∈ ℕ can be generated by at most n²/2 + 9n/2 + 7 surjective functions of the same set; and there exist n²/2 + 9n/2 + 7 surjective functions that cannot be generated by any smaller number of surjections. We also present several analogous results for other classical infinite transformation semigroups such as the injective functions, the Baer-Levi semigroups, and the Schützenberger monoids.
The paper contains characterizations of generators and cyclic projective generators in the category of ordered right acts over an ordered monoid.