Black and White take turns claiming cells. Black wins by owning all six cells of a Snaky, the hexomino on the left, in any rotation or reflection. White wins by stopping that until the board is full; White's own shapes don't count. Black moves first. You are White.
Black plays Nándor Sieben's proof sequence for Snaky (October 2026, nandorsieben/Snaky), built from the strategies in OpenAI's Snaky in 21 Maker moves. It wins within 20 Black moves, one fewer than OpenAI's 21, and every Black stone and every cell it relies on lies in a 251-cell region that fits a 17 × 17 board.
For this page his 1,510 situations were converted into 1,738 cards in the format of
the 15 × 15 page: "Black owns these cells, White has nothing in this region,
Black plays here, and Black wins within h moves". The card checker from the 15 × 15
Lean proof (cardcheck, the same checker compiled) accepts the converted set
on 17 × 17. The "promise" counter is the current card's height.