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cjjpeterson 41 ( +1 | -1 )
K-B-N checkmate My friend cj_leonine and I were playing a little otb today and came across this situation. We spent roughly 2 hours trying to find a strategy for a K-B-N checkmate. Is there a basic strategy to follow? Any info would be greatly appreciated. Thank you.

cjjpeterson
ganstaman 43 ( +1 | -1 )
There are many resources out there, and I'm sure others will post some of them. Personally, I love wikipedia for everything and the Xs in the diagrams are nice.

-> en.wikipedia.org

Enjoy. By the way, I've read all this before, but I can't do it (I don't think). One of those things that you learn really well, never use, and then completely forget. But have fun if you want.
far1ey 71 ( +1 | -1 )
This has never happened to me although I have spent a few hours by myself just toying with the situation. From this I gathered that you need the knight to cover the opposite coloured squares which the bishop covers. ie if you have a white squared bishop the knight should try cover the black squares. From there you make little "barriers" as shown in the wikipedia article given by ganstaman. During a game I would suggest that instead of trying to force the king into the corner/checkmate just work on getting a barrier up towards the corner which you will mate in. Then just walk the king over and mate.
ionadowman 165 ( +1 | -1 )
I've had this configuration... ... 3 times in offhand games, and won them all. But don't ask me the correct strategy. I was lucky in all 3 games that the enemy king was already confined to a fairly small sector of the board and couldn't get away.
First of all there are just 2 squares that checkmate can be forced on: the two corner squares that the bishop can reach (i.e. a1 and h8 for the dark=squared bishop, and h1 or a8 for the light-squared bishop). So the trick is to herd the king to one of those corners.
Bear in mind checkmate can be delivered on any edge square. This possibility helps drive the enemy K.For instance:

w

White plays 1.Be7+ Kg7 Black can not play 1...Ke8? on account of 2.Nd6# or 2.Nf6#
Now the BK is very close to the corner we want him at. But we can't let him escape via g6, h5 etc. So:
2.Ng3 ... the N and B have created a barrier along the 5th rank, whilst K and B guard the f-file.
2...Kg6
3.Bh4 Partly a waiting move, but also to vacate e7 for the WK
3...Kg7
4.Ke7 Kg6 A bid for freedom!
5.Kf8 Kh7 ...gains a tempo over Kh6, but that's all.
6.Kf7 Kh6
7.Bf6 Kh7
8.Bg5 Kh8 Now White manoeuvres his knight so that it reaches f8 with check
There are any number of routes you can take. The journey will take 4 moves:
9.Ne2 Kh7
10.Nd4 Kh8
11.Ne6 Kh7
12.Nf8+ Kh8
13.Bf6#

Suppose Black tried the tricky 4...Kg8!? White could play 5.Kf6, but he's really just marking time so doing. Preferable is
4...Kg8
5.Bf6 Kh7
6.Kf7 Kh6
7.Bh4 Kh7
8.Bg5 Kh8 arriving at the same position at move 8 in the other line.

It is possible that wikipedia will give a quicker mate from the diagram than I've shown here, I haven't checked. But, highly favourable though this position is for White, it does show the use of a mate threat to drive the enemy king, and how K, N and B create barriers driving the King into a corner.
Note that the checkmate by the bishop along the diagonal is the only one that can be forced.
Cheers,
Ion

spijker 35 ( +1 | -1 )
It seems correct what ionadowman writes, but it is possible to mate the king on a field that is not in a corner. It's is a fact that that kind of positions can not be forced.
See white: Kg3,Nf3 and Bd3. Black Kf1.
It is also possible to mate in a corner that is not of the color from the bishop.
White: Kc1,Bb1 en Nb3 Black Ka1. So you must always play carefull if you don't want to be mated!
ionadowman 36 ( +1 | -1 )
Those unforced mates... ... mentioned by spijker are worth knowing. They can be used, as the one illustrated in the 13-move mate above, as threats to further your cause. Here they are pictured:

b

or

b

Cheers -
wschmidt 11 ( +1 | -1 )
And, to pick up on a sensitive subject in another thread, you could spend some time using an online endgame tablebase to see how it's done!
ionadowman 96 ( +1 | -1 )
Indeed you could... ...as indeed I could have done with the position I posted on Jan 25th. But I didn't, nor did I consult wikipedia, though I had seen its article several months, maybe a year, ago.
I originally just wanted to set up the "unforced checkmate as threat" position, but then thought I'd just play it out. It turned out to be not hard, took maybe 5 minutes, yet had some nice, instructive, features in the 13 move sequence.
On the subject of this particular ending, wikipedia gives you a general strategy that helps you to set up blocks to the enemy king's escape. A TableBase like the Nalimov gives you particular moves.
Now it has been established that use of the latter is held to be the equivalent to using an engine if you are using it to determine moves in an ongoing game. But what about the wikipedia article? It does give a sample line (I'm going by memory here), but only as an illustration of the strategy you ought to follow. Is it OK to use that?
I think I'll repeat this question in the other thread...
kewms 27 ( +1 | -1 )
If the Wikipedia article is forbidden, so is every endgame book ever written. They all demonstrate the procedures for basic checkmates. It seems pretty clear from the Official Response in the other thread that banning endgame books was not the intent of the rule.


buddie 27 ( +1 | -1 )
Here's an example of the K+N+B v K ending in action.

board #3582174

The pure ending starts at move 102(!) if you don't want to replay the whole game.

By the way, anybody had a Gameknot game longer than 130 moves?