Sambo, U. ., U. . Adamu, B. . Sule, and M. A. . Yahaya. “Progressive and Retrogressive Phenomena of Economic Activity in Africa”. Journal of Asian Multicultural Research for Economy and Management Study, vol. 1, no. 2, Nov. 2020, pp. 7-18, doi:10.47616/jamrems.v1i2.42.