Draw by insufficient material

[Martin]

According to Wikipedia (http://en.wikipedia.org/wiki/Draw_(chess)) there is a draw by insufficient material if:

"king and bishop versus king and bishop with the bishops on the same color. (Any number of additional bishops of either color on the same color of square due to underpromotion do not affect the situation.)"

So not only K+B vs K+B with B's of the same color, but positions with _any_ number of B's of the same color.

I implemented this in recent versions of Anatoli, but now I'm doubting, is it really true?
Can an engine claim a draw by insufficient material in K+B vs K+B+B+B, for instance, if all B's are of the same color?
Of course such positions will rarely occur in games, but I would like to know.

The other question is, even if a draw claim is correct in such a case, will most or all tournament software accept it or flag it as "invalid draw claim" because the software only recognizes the case K+B vs K+B?

[hgm]

WinBoard would not recognize such a draw claim as valid. I did decide against putting that in, because it will not occur in practice, and because doing it would still not cover all draw cases. Because according to FIDE rules a game is draw if no mate is possible, not because of the material that is on the board. So K+4P vs K+4P can also be a legal draw. And it is actually a lot more likely than KBBKB. But there is no way a GUI is going to recognize that, so why bother with KBBKB?

[d] 4k3/8/8/p1p1p1p1/P1P1P1P1/8/8/4K3 w

[krazyken]

I suppose the best use of that knowledge, is that you can safely play instantly until you get a 3-rep or fifty move, and offer a draw every move

[bob]

WinBoard would not recognize such a draw claim as valid. I did decide against putting that in, because it will not occur in practice, and because doing it would still not cover all draw cases. Because according to FIDE rules a game is draw if no mate is possible, not because of the material that is on the board. So K+4P vs K+4P can also be a legal draw. And it is actually a lot more likely than KBBKB. But there is no way a GUI is going to recognize that, so why bother with KBBKB?

[d] 4k3/8/8/p1p1p1p1/P1P1P1P1/8/8/4K3 w

king and pawns is _never_ a draw. One side can always play stupidly and let the other side eat his pawns and promote. If there is one P on the board, draw due to insufficient material is not possible.

The actual rule is "position is drawn if no mate is possible, even if opponent plays the worst possible moves..."

There is no way to force mate with KB vs K, no matter how many B's of the same color you have. If the opponent has a B, of a different color, then things change, because his own B can restrict the king just enough to allow a mate, if he plays badly.

[michiguel]

WinBoard would not recognize such a draw claim as valid. I did decide against putting that in, because it will not occur in practice, and because doing it would still not cover all draw cases. Because according to FIDE rules a game is draw if no mate is possible, not because of the material that is on the board. So K+4P vs K+4P can also be a legal draw. And it is actually a lot more likely than KBBKB. But there is no way a GUI is going to recognize that, so why bother with KBBKB?

[d] 4k3/8/8/p1p1p1p1/P1P1P1P1/8/8/4K3 w

king and pawns is _never_ a draw. One side can always play stupidly and let the other side eat his pawns and promote. If there is one P on the board, draw due to insufficient material is not possible.

In this specific position, it is KPPPP vs KPPPP . Still, there is no possible mate because they cannot cross the fortress to take any pawn. So, the position is a draw.

Miguel

The actual rule is "position is drawn if no mate is possible, even if opponent plays the worst possible moves..."

There is no way to force mate with KB vs K, no matter how many B's of the same color you have. If the opponent has a B, of a different color, then things change, because his own B can restrict the king just enough to allow a mate, if he plays badly.

[Martin]

WinBoard would not recognize such a draw claim as valid. I did decide against putting that in, because it will not occur in practice, and because doing it would still not cover all draw cases. Because according to FIDE rules a game is draw if no mate is possible, not because of the material that is on the board. So K+4P vs K+4P can also be a legal draw. And it is actually a lot more likely than KBBKB. But there is no way a GUI is going to recognize that, so why bother with KBBKB?

Yes, agree, why bother?
To avoid any problems with WinBoard or another GUI I will remove this claim from my engine and let it only claim a draw for K+B vs K+B with B's of the same color.
Not that I ever saw something like K+B vs K+B+B with B's of the same color, but you never know ..

[hgm]

[d] 4k3/8/8/p1p1p1p1/P1P1P1P1/8/8/4K3 w

king and pawns is _never_ a draw. One side can always play stupidly and let the other side eat his pawns and promote. If there is one P on the board, draw due to insufficient material is not possible.

The actual rule is "position is drawn if no mate is possible, even if opponent plays the worst possible moves..."

Look again... How do the "worst possible moves" lead to a checkmate here, according to you?

[bob]

WinBoard would not recognize such a draw claim as valid. I did decide against putting that in, because it will not occur in practice, and because doing it would still not cover all draw cases. Because according to FIDE rules a game is draw if no mate is possible, not because of the material that is on the board. So K+4P vs K+4P can also be a legal draw. And it is actually a lot more likely than KBBKB. But there is no way a GUI is going to recognize that, so why bother with KBBKB?

[d] 4k3/8/8/p1p1p1p1/P1P1P1P1/8/8/4K3 w

king and pawns is _never_ a draw. One side can always play stupidly and let the other side eat his pawns and promote. If there is one P on the board, draw due to insufficient material is not possible.

In this specific position, it is KPPPP vs KPPPP . Still, there is no possible mate because they cannot cross the fortress to take any pawn. So, the position is a draw.

Miguel

The actual rule is "position is drawn if no mate is possible, even if opponent plays the worst possible moves..."

There is no way to force mate with KB vs K, no matter how many B's of the same color you have. If the opponent has a B, of a different color, then things change, because his own B can restrict the king just enough to allow a mate, if he plays badly.

OK, I would agree but I am not sure at all (my rule book is at the office) as to what a TD might say in this position...

The "insufficient material" rule excludes pawns, so it doesn't apply here. I think the appropriate rule would be the "draw offer / draw offer accepted"

[bob]

[d] 4k3/8/8/p1p1p1p1/P1P1P1P1/8/8/4K3 w

king and pawns is _never_ a draw. One side can always play stupidly and let the other side eat his pawns and promote. If there is one P on the board, draw due to insufficient material is not possible.

The actual rule is "position is drawn if no mate is possible, even if opponent plays the worst possible moves..."

Look again... How do the "worst possible moves" lead to a checkmate here, according to you?

In this position, they don't. But I do not believe the "insufficient material to force checkmate" applies. I don't have my rule book here at home, but I suspect the only rule that will apply is the rule about offering/accepting draws...

[sje]

Fide says:

10.4
The game is drawn when one of the following endings arises:

(a)
king against king;
(b)
king against king with only bishop or knight;
(c)
king and bishop against king and bishop, with both bishops on diagonals of the same colour.

This immediately ends the game.