Rook vs Pawn: Outflanking the King (Réti, 1928)

Réti's 1928 study packs two king techniques, shouldering and outflanking, into four moves.

Release the blockade. The rook sits in front of the pawn on d4 and the winning move is to leave: Rd2 or Rd3. Blocking on d1 is only a draw, and Rxd5+ is a dead draw as well.

Block again from further back. After 1...d4 the rook returns with 2.Rd1. The pawn is stopped once more, but it has committed itself, and White's king finally has something to aim at.

Outflank. 3.Kd7 is the only win: the king walks around its rival rather than into it. After 3...Kc4 4.Ke6 the pawn falls, and rook against a lone king is elementary.

Why zugzwang, of all things. Zugzwang is rare with a rook on the board, because a rook almost always has a harmless move to spare. The frontal blockade is the exception: tie the rook to the pawn's file and the kings are left in a pure opposition duel. That is why the winning idea is a rook tempo, Rd2 then Rd1, which hands the same mutual zugzwang back to Black. Keep the opposition as the defender and there is no way in; lose it for one move and the outflanking begins.