Conversion of advantage is much more complex with the pawns of the weaker side being blocked only on the fourth or the fifth rank. The winning strategy is again based on stalemating the opponent. We should note from the beginning that this is possible only if the king of the weaker side cannot penetrate into the drawing zone delimitated by the bishop’s diagonals c5-f2-h4; partially by the c-file i.e. c5-c7, and the rim of the chess-board d8-h8-h4. The simplest case, that is, when the enemy king has already been closed off by own pawns and cannot approach the drawing zone was analyzed by B. Horwitz as early as 1885.