# First move of wK (retrograde problem)

Ushkin
Posers and Puzzles 21 Aug '12 19:57
1. 21 Aug '12 19:57

First move of wK?
2. 23 Aug '12 22:49
Originally posted by Ushkin
[fen][6N1/4p2b/6pr/3P1p1k/5PRb/6pR/1PPPPPPq/2B1QK1n][/fen]
First move of wK?
The lazy mans answer is Kf1. I think the key to this problem is proving wether or not the h pawn ever moved.
3. SwissGambit
Caninus Interruptus
24 Aug '12 04:212 edits
Originally posted by tomtom232
The lazy mans answer is Kf1. I think the key to this problem is proving wether or not the h pawn ever moved.
0-0 is sexier. But I have a funny feeling that one of us is right. ðŸ˜›
4. SwissGambit
Caninus Interruptus
24 Aug '12 05:10
Originally posted by tomtom232
I think the key to this problem is proving wether or not the h pawn ever moved.
Both did. But I don't see how that solves the problem.
5. SwissGambit
Caninus Interruptus
24 Aug '12 06:38
5 wP captures + 10 black units on board = 15
1 bP capture + 14 white units on board = 15 + Bf1 died @ home = 16

There is one spare black piece to capture.

Getting black unlocked is difficult. g6 can't go back to g7 because Bh4 isn't home, and Bh4 is not promoted because there aren't enough available captures.

Sure, I could uncapture some black pawns on the d- and c- files, but that will only provide a few P tempii before black is stuck again. Right now he only has two useful moves, ...f6 and ...f7.

I am looking at shifting wQ/K left and bringing in a piece to shield on f1 so bQ can hide on g1 and Rh3 to h2 followed by yet another screen on h3 [where I'm going to get this piece, I don't know]. Then Bh4 goes home, ...g7, and Bh7 leaves, followed by Rh6 and bKh5. That should do it. I just need to think of a way to use two screens.
6. 24 Aug '12 23:222 edits
Can you use the white bishop on H1 as one of your screens? If the white king was there when the H1 bishop was taken, then it must have been taken by a black knight...

It is easy to show the white king did not take anything on his first move.

Can it be proved that white didn't castle, because perhaps then the capture by the white H pawn must happen too early for the position to work?
7. SwissGambit
Caninus Interruptus
25 Aug '12 13:46
Originally posted by iamatiger
It is easy to show the white king did not take anything on his first move.
It is?

I am looking at your idea of using wBf1 as a screen, BTW.
8. 27 Aug '12 05:582 edits
Hmm, proving the white king didn't take anything is harder than I thought. What I'm running into now is that assuming black doesn't run out of moves, and we get the shields in place to free up the blck's bishop, then white very quickly runs out of moves. We can't generate a white knight on g3 any time soon, because it puts black in check.
9. SwissGambit
Caninus Interruptus
27 Aug '12 13:25
Here's what I have so far.

Short by one tempo. White is stuck after black retracts Bf6.
10. 27 Aug '12 15:3910 edits
Originally posted by iamatiger
Hmm, proving the white king didn't take anything is harder than I thought. What I'm running into now is that assuming black doesn't run out of moves, and we get the shields in place to free up the blck's bishop, then [b]white very quickly runs out of moves. We can't generate a white knight on g3 any time soon, because it puts black in check.[/b]
I think it must be Kxf1,so I was totally wrong about the first move not being a capture! I'm looking at this position (A)

This reaches our position (forward) via

Kxf1, d6
Qe1, d5
cxd5

From (A) we can unwind (playing backwards) via
.. Qg1
Rh2 (untakes rook) Bf6
white pawn pack to b3(untakes pawn), black pawn back to H4 (untakes knight)
Ne4
giving

It looks like the position can be unwound from that start, black's knight can retreat from f1, untaking the white bishop, and then both black and white have knight moves available to lose any necessary tempos as the position winds back.

By the way, what's the best free way of constructing PGNs / FENs and fiddling with the board layout? I found
http://www.chess-poster.com/fen/epd_fen.htm
and
http://chessflash.com/chessflash.html

anything better than those?
11. 27 Aug '12 19:28
Oh Dear! That doesn't work because to get to f4, the white pawn has to take two black pieces which cannot be pawns, therefore the missing black rook and knight can't be on the board while that pawn is still on f4!
12. 27 Aug '12 21:5110 edits

we can work backwards with:
white pawn on d5 untakes a pawn
black bishop retreats to f6
white pawn on c4 untakes another pawn
black king moves into check on h4 (we are playing backwards, so this is ok)
White rook moves to G5 to uncheck king
Black king moves into check on G4
White rook moves to e5 to uncheck king

giving

Then it looks to me as if the position will unwind easily:

White and black both have free piecesto use up any tempos. The black h pawn gets to g3 by taking a knight; The white h pawn gets to f4 by taking two rooks, one of black's necessary 3 rooks is formed by black's a pawn promoting on a1 at some point
13. SwissGambit
Caninus Interruptus
28 Aug '12 01:26
Originally posted by iamatiger
I think it must be Kxf1,so I was totally wrong about the first move not being a capture! I'm looking at this position (A)

[fen]6N1/3pp2b/6pr/5p1k/2P2PRb/6pR/1PPPPPPq/2BQKn1n[/fen]
This reaches our position (forward) via

Kxf1, d6
Qe1, d5
cxd5

From (A) we can unwind (playing backwards) via
.. Qg1
Rh2 (untakes rook) Bf6
white pawn pack to b ...[text shortened]... tm
and
http://chessflash.com/chessflash.html

anything better than those?
I use WinBoard usually.

Looks like you solved it...good job.
14. 29 Aug '12 23:13
Bit of a joint effort really, your knight traverse inspired me.
15. 30 Aug '12 20:56
Originally posted by SwissGambit
Both did. But I don't see how that solves the problem.
If the h pawn never moved then 0-0 would be impossible.