Combinatorial results for certain semigroups of partial isometries of a finite chain. - Fatma Al-Kharousi; R. Kehinde; Abdullahi Umar (Australas. J Comb., 2014)

Combinatorial results for order-preserving partial injective contraction mappings. - Ahmed Bayo Musa; Nadia Aldhamri; Fatma Al-Kharousi; Georg Klein; Abdullahi Umar (Contributions Discret. Math., 2024)