AALI J. MOHAMMAD, ABDUL. “ON COLOURING MAPS & SEMIDIRECT PRODUCT GROUPOIDS ON GROUP-POSETS”. Journal of Education and Science (JES) 19, no. 2 (March 1, 2007): 99–109. Accessed August 4, 2025. https://rjps.uomosul.edu.iq/index.php/edusj/article/view/18092.