Introduction to additive combinatorics lecture 12.1 --- Finishing the proof of Roth's theorem

From a channel Lumen includes in full: Fields medallist Timothy Gowers works through olympiad and research-style problems live at the board, thinking aloud with all the false starts, plus lecture courses on topics such as additive combinatorics.

A 45-minute video from Timothy Gowers's catalogue; the title names its topic.

Video by Timothy Gowers, played through YouTube's embedded player.