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e f g 1 h ←→ to step through moves · Home / End — first / last Source
Why it works
The same pattern with colours reversed — this is the version YOU get to play. Black's 1...f6 weakens the e8–h5 diagonal, and 2...g5?? opens it completely. 3.Qh5# ends the game: the g5 pawn took away its own king's last hope of a ...g6 block. Whenever an opponent pushes both the f- and g-pawns early, check the h5 diagonal — the mate is often just sitting there.
Refutation
After 1...f6 Black is only slightly worse — but the follow-up must cover the diagonal: 2...e6 (or 2...e5, or a developing move like 2...Nc6) keeps ...g6 available as a block and the king safe. The rule of thumb: after moving the f-pawn, never touch the g-pawn until your king is castled.