m-POTENT ELEMENTS IN ORDER-PRESERVING TRANSFORMATION SEMIGROUPS AND ORDERED TREES

Let ?(n, r), ?(n, r), and ?(n, r) be the semigroups of s-potent elements in ?(n), the semigroup of order-preserving mappings, such that Fix()={1}, |Fix()|=1, and Fix() is arbitrary, respectively. We give combinatorial results relating the cardinalities |?(n, r)|, |?(n, r)|, and |?(n, r)|. We construct a correspondence between ?(n, r) and T-n,T- r the ordered trees with depth at most r and n nodes. Using this we produce generating functions for |?(n, r)|, |?(n, r)|.