On injective partial Catalan monoids

Abstract

Let $[n]$ be a finite chain $\{1, 2, \ldots, n\}$, and let $\mathcal{IC}_{n}$ be the semigroup consisting of all isotone and order-decreasing injective partial transformations on $[n]$. In addition, let $\mathcal{Q}^{\prime}_{n} = \{\alpha \in \mathcal{IC}_{n} : \, 1\not \in \text{Dom } \alpha\}$ be the subsemigroup of $\mathcal{IC}_{n}$, consisting of all transformations in $\mathcal{IC}_{n}$, each of whose domains does not contain $1$. For $1 \leq p \leq n$, let $K(n,p) = \{\alpha \in \mathcal{IC}_{n} : \, |\text{Im }\, \alpha| \leq p\}$ and $M(n,p) = \{\alpha \in \mathcal{Q}^{\prime}_{n} : \, |\text{Im } \, \alpha| \leq p\}$ be the two-sided ideals of $\mathcal{IC}_{n}$ and $\mathcal{Q}^{\prime}_{n}$, respectively. Moreover, let ${RIC}_{p}(n)$ and ${RQ}^{\prime}_{p}(n)$ denote the Rees quotients of $K(n,p)$ and $M(n,p)$, respectively. It is shown in this article that for any \( S \in \{ \mathcal{RIC}_{p}(n), K(n,p) \} \), \( S \) is abundant; \( \mathcal{IC}_{n} \) is ample; and for any \( S \in \{ \mathcal{Q}^{\prime}_{n}, \mathcal{RQ}^{\prime}_{p}(n), M(n,p) \} \), \( S \) is right abundant for all values of \( n \), but not left abundant for \( n \geq 2 \). Furthermore, the ranks of the Rees quotients ${RIC}_{p}(n)$ and ${RQ}^{\prime}_{p}(n)$ are shown to be equal to the ranks of the two-sided ideals $K(n,p)$ and $M(n,p)$, respectively. These ranks are found to be $\binom{n}{p}+(n-1)\binom{n-2}{p-1}$ and $\binom{n}{p}+(n-2)\binom{n-3}{p-1}$, respectively. In addition, the ranks of the semigroups $\mathcal{IC}_{n}$ and $\mathcal{Q}^{\prime}_{n}$ were found to be $2n$ and $n^{2}-3n+4$, respectively. Finally, we characterize all the maximal subsemigroups of $\mathcal{IC}_{n}$ and $\mathcal{Q}^{\prime}_{n}$.