Gul, Rizwan. “An Extension of VIKOR Approach for MCDM Using Bipolar Fuzzy Preference δ-Covering Based Bipolar Fuzzy Rough Set Model”. Spectrum of Operational Research 2, no. 1 (January 1, 2025): 72–91. Accessed May 31, 2026. http://sor-journal.org/index.php/sor/article/view/11.