Nisa, K., Sarifah, I. and Riyadi, R. 2026. COMBINATION OF CONTENT VALIDITY INDEX AND FUZZY DELPHI FOR EXPERT VALIDATION OF A THREE-TIER MATHEMATICS LEARNING DIFFICULTIES DIAGNOSTIC ASSESSMENT. BAREKENG: Jurnal Ilmu Matematika dan Terapan. 20, 4 (Aug. 2026), 3423-3436. DOI:https://doi.org/10.30598/barekengvol20iss4pp3423-3436.