In today's position, composed by Leonid Kubbel in 1925, White already has a pawn on the seventh, but it faces imminent death. Materially behind, White must make something of that pawn, but the only way to avoid losing it is 1. Nb5, putting the knight on a square where it may be taken by three pieces. Just the sort of thing we're looking for] So let's look closer: After 1. Nb5, what does Black play? 1 . . . Qxb5 loses to 2. Bc5+ followed by a8=Q; 1 . . . cxb5 allows 2. Bc5+ Kc6 3. Kb8] and the pawn promotes next move; 1 . . . Kxb5 is met by 2. Kb8 and again Black's queen is unable to prevent the success promotion of the pawn. So after 1. Nb5, Black cannot capture the knight after all. Meanwhile, White threatens 2. Bc5+ Kxb5 3. Kb8 forcing the win.
1. Nb5 is brilliant, unexpected, a three-way knight sacrifice, and the wrong answer. Unfortunately 1. Nb5 loses to 1 . . . Qa6+] After 2. Kd8 (2. Kb8 allows mate in one) cxb5 3. Bc5+ Kb7 Black is winning. Regrettably, we must abandon 1. Nb5.
The only other forcing move is 1. Nc4+, when 1 . . . Kb5 loses to 2. Kb8, but what do we do after 1 . . . Kxa7? It has to be 2. Bc5+ Ka6 (Ka8 loses to Nb6+) and now all it needs is a little inspiration. The king on a6 is immune from a knight check for at least three moves, and Black threatens either Qb5 or Qxc2.
There is a move that stops both of those, and once you spot it, the problem is solved. After 3. Na3]] Black runs out of moves. 3 . . . Qxa3 loses to 4. b5+] Kxb5 5. Bxa3 Kc4 6. Bb2] and the ingenious 3 . . . Qb3, hoping for stalemate after 4. cxb3, is met by 4. b5+] with capture of the queen on the following move.
Kubbel composed dozen of ingenious problems in which a black queen was rendered impotent against lesser forces. This is one of his more lightweight examples but particularly neat in including the temptation of 1. Nb5, hiding a more subtle solution.
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