Maximal subsemigroups and finiteness conditions on transformation semigroups with fixed sets

Authors: YANISA CHAIYA, PREEYANUCH HONYAM, JINTANA SANWONG

Abstract: Let $Y$ be a fixed subset of a nonempty set $X$ and let $Fix(X,Y)$ be the set of all self maps on $X$ which fix all elements in $Y$. Then under the composition of maps, $Fix(X,Y)$ is a regular monoid. In this paper, we prove that there are only three types of maximal subsemigroups of $Fix\left(X,Y\right)$ and these maximal subsemigroups coincide with the maximal regular subsemigroups when $X\setminus Y$ is a finite set with $|X\setminus Y|\geq 2$. We also give necessary and sufficient conditions for $Fix(X,Y)$ to be factorizable, unit-regular, and directly finite.

Keywords: Transformation semigroup with fixed set, maximal subsemigroup, maximal regular subsemigroup, factorizable, unit-regular, directly finite

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