Winboard Forum

The position below is currently played in RWBC!
I have seen quickly it is a draw, but which engines do know this?

Note R vs. f2 pawn is dead draw and R vs. B sac is draw too as
long the Black king stays in the square of the h-pawn.

Guenther

[diag]8/8/5k2/8/2B4p/5RbP/5pP1/7K b[/diag]

I am not sure that it is a draw and the question is if white cannot force some zugzwang(for example if white get the rook to f7 when the black king is at h8 black is in zugzwang and lose a pawn).

Uri

Uri Blass wrote:I am not sure that it is a draw and the question is if white cannot force some zugzwang(for example if white get the rook to f7 when the black king is at h8 black is in zugzwang and lose a pawn).

Uri

The white king is out of play, rook and bishop can't mate the black king.
After the RxB king can't move, the position is draw.

No need to mate the black king.

If rook and bishop are strong enough to force it to a zugzwang then it is enough to win.

The fact that I do not see a way that they can do it is no proof that they cannot do it.

Some table with right square for the black king for every 2 squares of the white rook and white bishop may prove the draw but I have no time to analyze in order to do it.

Uri

Uri Blass wrote:No need to mate the black king.

If rook and bishop are strong enough to force it to a zugzwang then it is enough to win.

The fact that I do not see a way that they can do it is no proof that they cannot do it.

Some table with right square for the black king for every 2 squares of the white rook and white bishop may prove the draw but I have no time to analyze in order to do it.

Uri

The rook and bishop can't force the black king away from the center.
After Ke5 black king stays in the center, don't froget the promoting threat,
the bishop or the rook have to controll f1.

the winning line for white begins after ...Ke5 with Rf8, Rg8 Rg4 and h4 winning the black bishop by advancing the h-pawn. The rest is simple.

TL wrote:the winning line for white begins after ...Ke5 with Rf8, Rg8 Rg4 and h4 winning the black bishop by advancing the h-pawn. The rest is simple.

No, it's not so simple. How you advance h pawn when Black's bishop is at h4?
If you move the g-pawn Black can catch it with bishop and get a draw because .... h8 square is black.

Igor

TL wrote:the winning line for white begins after ...Ke5 with Rf8, Rg8 Rg4 and h4 winning the black bishop by advancing the h-pawn. The rest is simple.

Hi, "TL",

either you have overlooked that there is a black pawn on h4, or you have not been aware that black is not forced to move its bishop away from g3. Both means that white cannot move to h4 without sacrificing his rook, which immediately leads to a draw.

My conclusion: it's a draw because the black king stays on central fields (as pointed out by "smith72") and does not get into a zugzwang position which would force him into an uncovered check. The latter is definitely not possible for the following reason (I try to give a full description to satisfy also Uri ):

There are only two configurations of wR, wB and bK with black to move and black being forced to move into an uncovered check which wins the Pf2:
1) wRf7, wBe6/d5/c4/b3/a2, bKh8; black would have to move Kg8 (as pointed out by Uri)
2) wRc2, wBd3 (must observe f1), bKa1; black would have to move Kb1

Other configurations with wR on f file do not enforce this because bK either can't move into an uncovered check by the rook, or bK always has at least one possible move to a black square (and possibly to other safe white squares). See the following "table" to show all relevant cases for the latter:

Rf7/f5/f3 and bishop on g/h file: bK has too many possible squares
Rf7, Be8: Kh6->g5, Kg6->h6/g5, Kh5->h6/g5, Kg5->h6
Rf5, Be4/d3/c2/b1: Kh6->g7, Kg6->h6/g7, Kh7->h6/g7/h8, Kg7->h6/h8, Kh8->g7, Kg8->g7/h8
Rf5, Be6/d7/c8: not possible (bKg4 illegal)
Rf3, Be2/d1: same as for Rf5 with Kh6/g6/.../h8/g8; Kh5->g5/h6, Kg5->h6

Other configurations with wR on rank 2 do not fulfill the condition to control f1 which must be done by the bishop here.

Enforcing one of the configurations 1 or 2 is not possible because it is not possible to force the enemy king to any border square with only rook and bishop but without using the own king, provided the enemy king is not yet located on a border square. The latter holds because black can move Ke5 in the given position.

I hope I did not forget anything, because I wrote this without using any (electronic or real) chess board.

Sven

ups, i had changed the the squares of the black bishop and the h-pawn.

A fen string is a very fine thing.

TL wrote:A fen string is a very fine thing.

You can get the FEN-string (even if it?s not posted under the diagram), if you click on ?Quote? (?Zitat?) of the posting - here you see and copy it!

Regards,
Franz.