# Chess Construction Challenge #3-The Inverse Babson

Today's challenge is to construct four positions, with White to move and win, such that:

1. In each position, White's move is to promote to a particular piece, for a position per promotion choice.

2. Black's next best move is to promote to a piece, and Black promotes to the same piece that White does.

3. Therefore, White may not promote with check, but Black can

4. The position must be legal, and FIDE laws of chess apply.

The real challenge is that you must use as few pieces as possible for each position. You must also state both White's and Black's motivation for their promotion.

Good luck!

• congrats on 2.5k rep! – Omega Krypton Sep 23 at 13:16
• @OmegaKrypton Thanks! :-) – Rewan Demontay Sep 23 at 13:48
• @RewanDemontay "Black's next best move is to promote to a piece" What exactly is the definition of a next best move? The move that should allow black to live the longest? The problem states that white's move is winning, meaning that all of black's moves by definition are equally bad at the goal of not losing the game, and are equivalent to just conceding. – Cruncher Sep 23 at 17:18
• @Cruncher Black's "best move" is whatever the optimal defense is. It does not matter if Black is 100% losing-in chess problems, the best defense is always employed. So your last sentence is irrelevant. No two defense are always equal. – Rewan Demontay Sep 23 at 17:21

For promotion to queen, a solution with four pieces:

Best play is

1. b8=Q a1=Q; White could also play Kb2 to win but that takes a move longer. Black should promote since it forces White to win the piece with 2. Qa8+ or Qa7+, giving the black king the chance to escape (temporarily). Black could also promote to a rook, that would be equivalent; I'm not sure if this disqualifies the position, but it will be hard to find one with less pieces.

For promotion to knight, one with nine pieces:

The solution here is

1. e8=N, threatening mate in one; the only way for Black to postpone this is by a check, which can only be done with 1... h1=N+. White will win anyway with 3. Nc7#.

• Well, technically, Black’s best move is to promote to a queen, so promoting to a rook is irrelevant in this case, – Rewan Demontay Sep 23 at 13:47
• Practically speaking, yes, but technically both moves are best. That is not allowed for some kind of chess problems but you set the rules :) – Glorfindel Sep 23 at 13:49
• Yup! Feel free to find a position with a unique queen promotion if you want to! – Rewan Demontay Sep 23 at 13:53
• Still puzzling over this? That’s okay! – Rewan Demontay Sep 24 at 18:39
• Heh, it's hard enough finding positions where promoting to bishop or rook is the strongest move, I'm not a problemist. I might be able to find positions where it doesn't matter (for the distance to mate) if you promote to a bishop or a queen, but I wouldn't be satisfied with those. – Glorfindel Sep 24 at 19:02

Promotions to knights, 8 pieces

White to play and mate in 3.

Solution:

1. e8N! f1N! (any other move allows a faster mate with 2.Ng7#) 2. Kh3! a.l. 3. Ng7#/Nf6#

Nobody has a offered a bishop construction yet. Here is one, though imperfect:

White to move and mate in 3

Solution:

1.b8B a1B 2.Bf4 g3 3.xg3#

It is not great because

Although 1...a1B limits White choice, and it would have prevented the #3 in case of 1.b8Q?, it is not technically "better" than 1...a1Q

The difficulty to build a problem with BB or RR promotions is that

We need two stalemating ideas: one that is avoided by White's underpromotion, and a second one which makes Black's underpromotion better than a Q-promotion and allows him to postpone the mate. Most probably, it will require a #4 stipulation to have both underpromotions on the first move.

• Unfortunately, your #3 is cooked: 1. b8=B a1=Q 2. Bxf4 Qxa3 3. Bg3+ Qxg3 4. fxg3#. which allows for 1. b8=Q a1=B 2. Qe5 g3 3. fxg3+ fxg3 4. hxg3#. – Rewan Demontay Oct 7 at 16:02
• @RewanDemontay Fixed, thanks. – Evargalo Oct 8 at 6:18
• You're welcome. You should combine your two answers, please. I only have one checkmark to give out when a full answer is given at some point. – Rewan Demontay Oct 27 at 5:04

Promotion to rook, 5 pieces (note this may not qualify)

FEN: 8/7P/8/8/8/K7/1p1N4/k7 w - - 0 1

The strongest move for White is 1.h7-h8=R (since the queen/bishop promotions stalemates Black, and the knight is obviously not enough (actually, after 1.h7-h8=N one of the best moves for Black is 1...b2-b1=N+, forking White's king and knight so forcing an exchange - kind of same-piece promotion in a side variation)). After that, 1...b2-b1=R is one of the best moves for Black, unfortunately alongside with 1...b2-b1=Q (so I write above that it probably does not qualify). Note that 1...b2-b1=B is worse, since it allows immediate checkmate with 2.Nd2-b3#. After 1...b2-b1=Q(R) follows 2.Nd2-b3+ Q(R)b1xb3+ 3.Ka3xb3 Ka1-b1 4.Rh8-h1# (or 1...b2-b1=N+ 2.Nd2xb1 Ka1xb1 3.Rh8-c8 Kb1-a1 4.Rc8-c1#).

• Eh I really wouldn’t qualify this one. You said so yourself. – Rewan Demontay Oct 3 at 11:20

I believe this qualifies:

White, in an attempt to smother-mate Black's king, plays 1. e8N. To save the draw, Black then is forced to respond with a check 1... f8N+. (Note that the white king marching to capture the black pawn does not work due to the risk of stalemate.) After the king moves to a square, let's say g2, the game continues 2. Kg2 Nxf3. White is forced to play 3. Kxf3 and take the draw, else lose against a large pawn mass.
Follow-up after my original thoughts: After some thought, White may be able to play 1. e8Q and try to get the queen to h1 or h2. Black then responds 1... f8Q, and will play next turn one of Qg1+, Qg2+, or Qh1+ to draw.