Введение в математический анализ 21. Выпуклость функций.

Whole-channel inclusion: Лекторий ФПМИ is an honest teaching channel (title sample + 3 transcripts read: The transcripts show genuine sequential university lectures with rigorous mathematical content delivered by named instructors, consistent with the 'whole' verdict.); this title passed a strict title check (sonnet) after a labelling pass.