legal AND illegal positions
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Feb 9, 2011
0
#82
pompom wrote:
einstein_69101 wrote:
I think this is illegal, but I'm still working through the thoughts. Here is the diagram:
I agree with the fact that white needs to play e3, axb3 and bxc4 in order to give the bishop room to move to b1 from f1. Since this is a light bishop, the only way for it to make it is to play Ba4 -> Bb3 (after axb3 and bxc4 are played) -> Ba2 -> Bb1. White needs to execute this plan before black puts his bishop on a4.
The white pawn on c4 comes from the a2-square because axb3 and bxc4 is the only way for both a2 and b3 to be free for the light bishop to make its journey. This means the pawn on b3 comes from the b2-square. The a-file is the only file that comes open for white's rooks to come out. The white rooks need to come out before black plays Ra2.
One thing that was not mentioned was the fact that white needs to play Na1 before he plays b3. Otherwise the knight will never get there. Similiarly, black needs to play Nh8 before g6 is played. And white's dark bishop cannot get out until white plays b3. White's queenside rook can move out of the way, but the other rook needs to escape as well. White's kingside rook cannot get out until white's knights, bishops,queen and king clears the way. It would have to come out by playing Rb1 -> Rb2 -> Ra2 because the dark bishop cannot get out until white plays Na1 and b3 first.
b6 was never played (with a black pawn on a7) because black's dark bishop would never have a chance to reach b8. However, b6 does get played once the dark bishop reaches a7 (or b8) so that black can free the light bishop. This means that white's king can only reach black's backrank via g7. In order for black to allow white to play Kh6 -> Kg7, black needs to play Nh8 and g6 first. White's king needs to travel all the way across the backrank to b7 so that black can get one of his rooks back to g7.
Those facts are true, but one player could always waste time by moving a piece back and forth.
That is true. There is a lot of traffic in the a1-corner that makes it tricky for that position to be reached. It looks like black needs to play Ba4 before he puts a pawn on b5. It seems like axb5 is the only way to put a pawn there after Ba4. But if black did this before he frees up one rook, then black cannot free up a rook so it can reach a2. And if black don't play axb5, then his rook is trapped by his pawns. If black plays axb5 to free up one rook, then black can never get his bishop to a4 (The white pawn on c4 blocks off the other path to a4.)
Edit: Black might have some time to play Bb3 after Ba4 to free up the rook if white has not played b3 yet, but this means that white's dark bishop is still stuck on its starting square. I'm still thinking through it. :)
einstein_69101 wrote:
I think this is illegal, but I'm still working through the thoughts. Here is the diagram from post #24:
I agree with the fact that white needs to play e3, axb3 and bxc4 in order to give the bishop room to move to b1 from f1. Since this is a light bishop, the only way for it to make it is to play Ba4 -> Bb3 (after axb3 and bxc4 are played) -> Ba2 -> Bb1. White needs to execute this plan before black puts his bishop on a4.
The white pawn on c4 comes from the a2-square because axb3 and bxc4 is the only way for both a2 and b3 to be free for the light bishop to make its journey. This means the pawn on b3 comes from the b2-square. The a-file is the only file that comes open for white's rooks to come out. The white rooks need to come out before black plays Ra2.
One thing that was not mentioned was the fact that white needs to play Na1 before he plays b3. Otherwise the knight will never get there. Similiarly, black needs to play Nh8 before g6 is played. And white's dark bishop cannot get out until white plays b3. White's queenside rook can move out of the way, but the other rook needs to escape as well. White's kingside rook cannot get out until white's knights, bishops,queen and king clears the way. It would have to come out by playing Rb1 -> Rb2 -> Ra2 because the dark bishop cannot get out until white plays Na1 and b3 first.
b6 was never played (with a black pawn on a7) because black's dark bishop would never have a chance to reach b8. However, b6 does get played once the dark bishop reaches a7 (or b8) so that black can free the light bishop. This means that white's king can only reach black's backrank via g7. In order for black to allow white to play Kh6 -> Kg7, black needs to play Nh8 and g6 first. White's king needs to travel all the way across the backrank to b7 so that black can get one of his rooks back to g7.
I tweaked Blackadder's attempt a little farther, but I'd say the position is illegal. The black king can't reach a1 since white's rook gets in the way. The white rook will have to be in the corner and the black rook blocking the white's rook attack from the king, and the king could go to e2. But in order for the king to go farther, both rooks will have to be cramped up in the a3-a2-b2 area. Then the king could reach the corner.
But then, white's rook will have to get behind black's rook. In order to do that, white's rook will have to be on e2. However, there's no way to do that without checking the black king. The black rook is trapped behind white's rook, so it couldn't block the king. There are no other black or white pieces that could help block the king. So, there would be no way for the white rook to get behind the black rook.
Nice puzzle! That was pretty hard.
Feb 9, 2011
0
#84
I tweaked Blackadder's attempt a little farther, but I'd say the position is illegal. The black king can't reach a1 since white's rook gets in the way. The white rook will have to be in the corner and the black rook blocking the white's rook attack from the king, and the king could go to e2. But in order for the king to go farther, both rooks will have to be cramped up in the a3-a2-b2 area. Then the king could reach the corner.
But then, white's rook will have to get behind black's rook. In order to do that, white's rook will have to be on e2. However, there's no way to do that without checking the black king. The black rook is trapped behind white's rook, so it couldn't block the king. There are no other black or white pieces that could help block the king. So, there would be no way for the white rook to get behind the black rook.
Nice puzzle! That was pretty hard.
I agree. It is a good puzzle. :)
Legal or illegal?
Actually, here's a "longer" version of the problem:
Legal or illegal?
Do you think this position is legal or illegal?
Servietsky wrote:
Do you think this position is legal or illegal?
I'm sure it's illegal in Alabama.
Legal or illegal?
pompom wrote:
I tweaked Blackadder's attempt a little farther, but I'd say the position is illegal. The black king can't reach a1 since white's rook gets in the way. The white rook will have to be in the corner and the black rook blocking the white's rook attack from the king, and the king could go to e2. But in order for the king to go farther, both rooks will have to be cramped up in the a3-a2-b2 area. Then the king could reach the corner.
But then, white's rook will have to get behind black's rook. In order to do that, white's rook will have to be on e2. However, there's no way to do that without checking the black king. The black rook is trapped behind white's rook, so it couldn't block the king. There are no other black or white pieces that could help block the king. So, there would be no way for the white rook to get behind the black rook.
Nice puzzle! That was pretty hard.
Actually, the position in question (from post #24) is legal, and relatively easy to reach (see proof game below). I highlighted your mistake: you forgot about the White king!
Feb 12, 2011
0
#95
TheGrobe wrote:
This one is legal assuming that the a1 square is in the lower left-hand corner.
cobra91 wrote:
pompom wrote:
I tweaked Blackadder's attempt a little farther, but I'd say the position is illegal. The black king can't reach a1 since white's rook gets in the way. The white rook will have to be in the corner and the black rook blocking the white's rook attack from the king, and the king could go to e2. But in order for the king to go farther, both rooks will have to be cramped up in the a3-a2-b2 area. Then the king could reach the corner.
But then, white's rook will have to get behind black's rook. In order to do that, white's rook will have to be on e2. However, there's no way to do that without checking the black king. The black rook is trapped behind white's rook, so it couldn't block the king. There are no other black or white pieces that could help block the king. So, there would be no way for the white rook to get behind the black rook.
Nice puzzle! That was pretty hard.
Actually, the position in question (from post #24) is legal, and relatively easy to reach (see proof game below). I highlighted your mistake: you forgot about the White king!
Ah, yes. I forgot about that. I didn't really want to directly say that the position is illegal, since I'm not really sure yet and that I thought there was something lurking around that I'm not seeing.
Servietsky wrote:
Do you think this position is legal or illegal?
Hmm... I'm not sure yet. I'll have to work that problem out.
The position in post #92 is also legal:
cobra91 wrote:
The position in post #92 is also legal:
Correct.
