Sandwich sets and partial order.
Schützenberger groups and Chebyshev polynomials.
Schützenberger groups of ...-classes in the semigroup of all binary relations on a set.
Schützenberger groups of some even degree polynomials in S(R).
Second centralizers of partial transformations
Second centralizers of partial transformations on a finite set are determined. In particular, it is shown that the second centralizer of any partial transformation consists of partial transformations that are locally powers of .
Semi-automorphisms of transformation semigroups
Semigroups for which the continuum congruences form finite chains.
Semigroups in which ... and ... coincide for regular elements.
Semigroups in which each -class contains at most one regular ...-class.
Semigroups of ...-density continuous functions.
Semigroups of finite matrices.
Semigroups of mappings on graphs.
Semigroups of order preserving mappings on a finite chain: a new class of divisors.
Semigroups of order-decreasing transformations: the isomorphism theorem.
Semigroups of order-preserving partial endomorphisms on trees, I
Semigroups of transformations restricted by an equivalence
Suppose σ is an equivalence on a set X and let E(X, σ) denote the semigroup (under composition) of all α: X → X such that σ ⊆ α ∘ α −1. Here we characterise Green’s relations and ideals in E(X, σ). This is analogous to recent work by Sullivan on K(V, W), the semigroup (under composition) of all linear transformations β of a vector space V such that W ⊆ ker β, where W is a fixed subspace of V.
Semigroups whose regular ... -classes form well-ordered chains.
Semigroups whose regular J-classes form finite lattices.
Semigroups with exactly three regular ...-classes.
Semigroups with only finitely many regular ... -classes.