We define, for any special matching of a finite graded poset, an idempotent, regressive and order preserving function. consider the monoid generated by such functions. call idempotent element this monoid. They are interval retracts. Some them realize kind parabolic map called projections. prove that, in Eulerian posets, image projection, its complement, induced subposets. In Coxeter group, all ...

Call a sum of exponentials of the form f(x) = exp (2πiN1x) + exp (2πiN2x) + · · ·+ exp (2πiNmx), where the Nk are distinct integers, an idempotent. We have L interval concentration if there is a positive constant a, depending only on p, such that for each interval I ⊂ [0, 1] there is an idempotent f so that R I |f (x)| dx R 1 0 |f (x)| dx > a. We will explain how to produce such concentration f...

Our paper is inspired by the paper [3] by M. Nathanson, in which he considers iteration of the process of adjoining identities or zeros to semigroups and characterizes the resulting semigroup in the case when one starts with the trivial semigroup. We consider also the third type of adjoining, namely, we adjoin idempotents “that behave like some already existing elements.” We investigate the pro...