1. Department of Mathematical Sciences, The Citadel, Charleston, SC, USA Email address:
2. School of Maths, Wits University, South Africa, Research Group in Algebraic Structures and Applications, King Abdulaziz University, Saudi Arabia and Centro de Ciencias Matemáticas UNAM, Morelia, Mexico Email address:
3. Department of Mathematics and Statistics, University of Calgary, Calgary, AB T2N 1N4, Canada. Email address: