NISA, K.; SARIFAH, I.; RIYADI, R. 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, v. 20, n. 4, p. 3423-3436, 24 ago. 2026.