possible or impossible?

Maybe it's for the best, since now people can't copy what you already did and try to find a small improvement that you missed

I'll try to do this now.

Ok, I analysed the position for quite a bit and looked at many different ideas. Unfortunately, many did not seem to work.

I managed to get 54 moves rather quickly, but then finding an improvement became much more difficult. Eventually I found a way to get 53 moves which, I believe is the best possible.

Can anyone find 54 or 53 moves? or god forbid, a better score

Also, here's a guideline on how to approach the puzzles in #163:

1) Can black get all of those promoted pieces?

2) What were the last moves?

I will also give a small hint straight away regarding which position is legal, to encourage people to try (highlight to see): Position 1 is illegal and position 2 is legal. So you might want to work on that one.

 If no one seems interested (or has given up) in trying, I will post the solution!

I got the 53 eventually, will try for 52 now :)

Impressive! I wonder if we used the same method. I couldn't figure out a way to get 52, but I've seen crazier things happen!

My method was (highlight to see)

Shift all the white pieces along one to allow athe rooks on one side of the board an extra square for maneuvring

I think 52 is impossible but don't know. I might have a go at that #163 tomorrow now I've got a hint to help me :)

Yeah I think so too. We also probably used the same method to reach 53 moves. Here's mine:

52 , the white first-rank-shifting was unneccesary but I had put it in anyway and didnt feel like re-entering the game

For #163 the last white move must have been a pawn move (or for #1 1.Rh5+ N4xh5# but I doubt the composer left any spare white pieces)

In position 2 Black can play N4h5# with the same position as #1 except for a rook. But I have no idea why f5 would be a legal rook position and c4 not, I suppose I'll only figure out if i do loads of analysis of the position

Haha brilliant! switching rooks to opposite wings. Now that's creative thinking.

Could white have moved a pawn on his last move though? This can be easily determined if you try to actually obtain all of those promoted pieces for black.

And if white couldn't have, what could have been his last move? What was the last sequence?

Let me know if you're still working on it, because it seems at the moment like you're the only one :)

There are 5 white pieces that can be captured (Q,R,R,N,black bishop)

The d-pawn made 2 captures, the other pawns 1.

the b-pawn must have moved to allow cxb2

If the a-pawn was on a3 until the previous move then it must have moved before the b-pawn to allow bxa2, but the b-pawn must have moved first to allow axb2.

Contradiction, therefore the a-pawn was on a4 and b-pawn on b3 and the last white move was not a pawn move

White has just moved, his last move was not a pawn or knight move therefore it was a king move.

If this was being played 20 years ago then it would have been easily possible because a king was only considered in check if attacked by 1 or 2 pieces. So it would not have been in check on f8. But under the current rules it is in an impossible triple check on f8.

So there must be trick that I'm missing.

(if it was white to move it would be possible with say B on c4, N on d5, K on g8, 1...Nd5-f6++ 2.Kg7 Bg8)

Here's a fresh one for you all. Double-check your answers... there are several tricky bits here.

Surely that is illegal because there is no way the rook can get to b3 without white already being in check?

So we have to reach this position with whatever white piece on a1.

The pawn in b2 come from g7. He has to take on f6, e5, d4, c3 and b2. So 5 times.

White is missing 2 rooks, 2 bishops, queen and 1 knight. One less to promote. So 5 pieces remaining.

The problem is white can't developp his white bishop.

I think it's not possible.

Very nice deductive work, zuup!

Now tell me if this version changes anything:

Now it is possible 

My argument become invalid! 0_o

But I don't have time to look more at it.

Good work, s0030135! 

You guys are demolishing my puzzles.