The final conclusion from the preceding example may have served as inspiration to J. Kling to compose a superb study on the theme of the importance of triangulation and a reserve tempo. Kling had demonstrated as early as 1848 that there is an exception with blockaded pawns on b/g file; that is, White wins only if his rook’s pawn is still on its initial position! In order to properly understand this position and the key points of the winning plan, we must right from the start take note of two vital facts: a ) When White places his king on b3 and threatens the breakthrough via a4, the black king should at least be at c6, that is, must not lag behind the white king more than a file; b ) The position is won if the white king can invade the fourth rank preserving a reserve pawn move a2-a3. The key to the solution is provided by the question: What would happen if in the position with the kings at b3/c6 Black were to move? Since stepping on the d-file is not possible because of Kb3 and a4, whilst on any other move the black king gets farther away from the fifth rank, the logical conclusion is that White will be able to invade the fourth rank and then win thanks to a reserve a-pawn tempo. The squares b3 and c6 are squares of mutual zugzwang! If we take one step back, we will easily note that the squares c3/d5 are also squares of mutual zugzwang since Black again loses if he has the move. That is, he cannot go to the e-file due to Kb3 and the subsequent a4, while if he retreats to the sixth rank White will play Kd4 and win due to the extra a-pawn move. Based on this introductory analysis we may deduce that the critical moment will occur when the black king gets near the “mined” squares c6/d5. Therefore, the first stage of the winning plan will be preparing the threat a4 thus guiding the black king towards the square c6.
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