Let us now examine positions with the black king imprisoned in the corner g7. Pay attention to the word imprisoned since the threat a7 with the winning backblow of the rook, the black king must not leave the safety area restricted to squares f7-f6-h6-h7. At first sight one can conclude that Black is helpless here because of the “play without king”. For that very reason, a real revolution in the theory of rook endgames with rim pawn was made by I. Vancura in his discovery of the side defence, presented in a study published in 1924. Black king has already taken his ideal position, so that after a potential a7 he would immediately draw by placing his rook after the pawn. Simultaneously, the attack on the pawn passivizes the opponent’s rook, and White is left only with attempts to move his king.