✓ Все тайны листа бумаги A4 | Математика вокруг нас | Борис Трушин

Whole-channel inclusion: Борис Трушин is an honest teaching channel (title sample + 3 transcripts read: The transcripts show structured, step-by-step worked math problem solutions typical of exam prep tutoring, consistent with genuine teaching content.); this title passed a strict title check (sonnet) after a labelling pass.