Board setup

FEN: B7/2pp4/8/PP2p3/K7/8/5k1b/8 w - - 0 1

The board contains only bishops, pawns, and kings. You're playing White, and it's your turn. How quickly can you force a mate, despite the material disadvantage?

Source: Valentin Rudenko, 2.hm Achalgazdra Kommunisti, 1956.

  • $\begingroup$ This is a tough situation, so long as black doesn't move their king to a white square, this'll end up being a stalemate. I'm sure there's a way to do it, but it's not immediately obvious to me. +1 $\endgroup$ – Taco タコス Aug 31 '18 at 20:41
  • $\begingroup$ Great puzzle! $(+1)$ $\endgroup$ – Mr Pie Sep 3 '18 at 0:25

I think the key is

To promote your pawn to a Queen first, and control the A8-H1 diagonal with the Q-B combo, as @PerpetualJ has mentioned.

The sequence of moves would probably start with

1. a6! (push the pawn) Bf4 (mobilize the Black bishop). We then need to block the black square diagonal g1-a7, since this is the best diagonal for Black to block the coronation with 2...Be3 next. Then we use a pawn to achieve this, using 2. b6. 2. ... cxb6 is then forced, otherwise 3. b7 crowns the pawn. Then 3. Kb5!! blocks the Black bishop from accessing a7. Black rushes the pawn with 3...e4 4. a7 e3. White needs to control the diagonal as we mentioned, they do this with 5. Bh1. Black keeps rushing with 5...e2 6. a8=Q e1=Q. Unfortunately it’s now too late for Black, because the Queen serves as a barrier for the Black King now! 7. Qf3+ forces 7...Kg1, and then the final blow is delivered with 8. Qg2#.

So I think the answer is

Mate in 8 (lol, it rhymes!)

Notice that

The first Black move 1...Bf4 with the intended 2...Be3 is necessary; moving the two pawns out of the way instead loses because 1. a6 c5? 2. a7 e4? 3. Bh1 creates an unstoppable a-pawn. 1...Bg1 has some merit, but ultimately fails because the Black king has to move out of the way; Ke3, Ke2, and Ke1 block the e-pawn; and Kf1 has the same effect as above except blocks the king in faster with 7. Qg2#.

  • 1
    $\begingroup$ Move 2 is the key, I couldn't figure how to prevent what you prevented, then I finally did but you'd already posted. $\endgroup$ – Joel Rondeau Aug 31 '18 at 21:20
  • 1
    $\begingroup$ What if black plays 6... e1=N? $\endgroup$ – isaacg Aug 31 '18 at 22:28
  • $\begingroup$ I think that's it. Haven't checked all the moves in detail, but this looks like the solution I had. $\endgroup$ – Rand al'Thor Sep 1 '18 at 10:48
  • $\begingroup$ @Randal'Thor isaacg has a point: why black would trap themselves by promoting to a queen? $\endgroup$ – xhienne Sep 2 '18 at 0:47
  • 1
    $\begingroup$ @xhienne for the sake of uncovering what happened, I searched up whether this puzzle was available online. The solution that Chess.com provides is here although I’ve not found anything further. I agree though that this seems not as well posed as others I’ve solved. $\endgroup$ – El-Guest Sep 2 '18 at 17:00

I would personally go on the assault to take other pieces.

Lead with your king, though you can't check with the king, you can take the pawns. You'll need to lure the black bishop and pawns into the h1-8 diagonal. So long as you're able to retain your pieces, the black king will eventually have no defense and will be forced to surrender or stalemate will eventually happen.

  • $\begingroup$ It would have been funny if you could make a perpetual check occur, hahah :P $\endgroup$ – Mr Pie Sep 7 '18 at 11:10

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