Aliyu, Z. H., and H. Ibrahim. “An Inventory Model for Non-Instantaneous Deteriorating Items Under Two-Phase Demand and Two-Level Trade Credit”. International Journal of Mathematical Sciences and Optimization: Theory and Applications 11, no. 3 (October 15, 2025): 108 -127. Accessed March 15, 2026. https://ijmso.unilag.edu.ng/article/view/2906.