A. Umar

activity

20102017

most citedA countable family of finitely presented infinite congruence-free monoids

2 citations · 3 across the 7 of their papers we have counts for

collaborators

7 papers

math.GR2017

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

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

Let $I_{n}$ be the symmetric inverse semigroup on $X_{n} = {1, 2, \dots, n}$ and let $DDP_{n}$ and $O DDP_{n}$ be its subsemigroups of order-decreasing partial isom…

math.GR2017

Presentations for subsemigroups of $P D_{n}$

Abdullahi Umar

Let $[n] = {1, \dots, n}$ be the $n$ -chain. We give presentations for the following transformation semigroups: the semigroup of full order-decreasing mappings of $[n]$ , the semigrou…

math.CO2013★ 1 cited

Lattice Paths and Order-preserving Partial Transformations

A. Laradji, A. Umar

Let $P O_{n}$ be the semigroup of all order-preserving partial transformations of a finite chain. It is shown that there exist bijections between the set of certain lattice pat…

math.GR2013★ 2 cited

A countable family of finitely presented infinite congruence-free monoids

Alan J. Cain, Victor Maltcev, Abdullahi Umar

We prove that monoids $Mon ⟨ a, b, c, d : a^{n} b = 0, a c = 1, d b = 1, d c = 1, d ab = 1, d a^{2} b = 1, \dots, d a^{n - 1} b = 1 ⟩$ are congruence-free for all $n \geq 1$ . This provides a ne…

math.CO2013

Constructing Even Order Magic Squares By Consecutive Numbering

A. M. Ibrahim, H. M. Jibril, A. Umar

The aim of this note is to introduce fastest new general methods for the construction of double and single even order magic squares. As in [5], the method for double even order mag…

math.GR2011

On the semigroup of order-decreasing partial isometries of a finite chain

R. Kehinde, S. O. Makanjuola, A. Umar

Let $I_{n}$ be the symmetric inverse semigroup on $X_{n} = {1, 2, ..., n}$ and let $DDP_{n}$ and $O DDP_{n}$ be its subsemigroups of order-decreasing partial isometrie…