Combinatorial results for certain semigroups of order-decreasing partial isometries of a finite chain

F. Al-Kharousi, R. Kehinde, A. Umar

Let ${\mathcal{I}}_n$ be the symmetric inverse semigroup on $X_n=\{1,2,\dots ,n\}$ and let ${\mathcal{DDP}}_n$ and ${\mathcal{O}\mathcal{DDP}}_n$ be its subsemigroups of order-decreasing partial isom…