Комбинаторика из олимпиады Физтех-2020 на изи | 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.