Mating With KNB vs. K

I thought I'd make a separate post on all cases I'm going to tackle, so here is the first one. Maybe it'll even help someone else, although I'm probably not going to get overly detailed where the matters are trivial to myself.

I've tried to learn KBN several times before, so I was not completely new to the ideas behind it. Drive the enemy king to the edge, force it to the corner the color of your bishop, and mate it. Sounds simple, but in practice the king just kept slipping away before I could get it into the right corner. Once in the correct corner, the mate is pretty straightforward after some thinking.

Also the driving to the edge -part is relatively easy, just 'oppose' the enemy king with your king, restrict with K&B until it has no legal moves but to retreat towards edge, and invade all the files/ranks it gives you until it's against the edge. It helps to remember that the enemy king's best defence is to first stay in the middle of the board, and that failing to retreat towards the wrong coloured corner. So these are the directions you want to block. In practice this also means that it's usually easiest to drive it towards the wrong corner to begin with. Another tip is to avoid placing a piece between the kings (sometimes it works though), so that you'll be able to snatch the files the enemy gives you without letting the him slip away. I didn't memorize any specific patterns for this phase, but after some drilling against Chessmaster it became instinctive and easy, and I'm now able to do that in a bullet game with no thinking whatsoever.

The thing that kept me baffled until I got some tips from Dragon Fire and Varenka on RHP, was the part where you drive the king towards the mating corner along the edge. The beginning is pretty easy, you just keep the enemy king against the edge with your king, build an additional 'wall' with the knight when needed, and block from 'behind' with the bishop so the king can't return. At some points you'll also need to lose a tempo with the bishop to get the enemy king where you want it.

But around the middle of the edge, you need to let the enemy king slip off towards the centre to herd it into the right corner. A sort of 'leap of faith' is required, which of course turns out to force the stray king back against the edge, when properly executed. The trick is to form a mating net from the king onward, only it's not possible to close the gap all the way to the edge, just up to a single square shy from it. It also looks like the net leaks badly at first glance, so it's a bit hard to visualize, but the bishop has time to block the remaining escape squares even farther to the middle, forcing the king back towards the edge. After that, it's again relatively easy to complete the journey towards the mating corner. -All this I pretty much worked out by myself, but there was one final trick that's needed for the net to hold: You need to start building it the knight one square from the edge, instead of moving it to the centre as seems intuitive. So Nb5! instead of Ne6 if you're driving the king from a1 to a8. After that, the king might try heading towards c8 which looks like a way out, but the bishop pounces over to the opposite flank to block it just in time. The net is still a bit sparse, and the king can turn back and try another break for the freedom via c6, but again the bishop is on time and the net closes up permanently. Nowhere to go but back towards the edge with all hope lost.

There is one more final little 'leap of faith' where you hang the knight for one move on Nb7+ to force the enemy king up, but it's easy to see and the attacking king simply moves one square up to defend the knight as the enemy king gets on striking distance.

Then it's only the mating itself left, so you just restrict the enemy king into two final squares, position the knight so that you can take the second to last square with check at will, lose a tempo with bishop to avoid stalemate if needed, then check and mate.

I personally like to set up a fixed position in the wrong corner to start the cattle drive, so I'll have a nice fixed series of 20 or so forcing moves up to the mate that I can blitz through. It's not the fastest way, and requires losing a tempo here and there, but it's systematic and reliable. There's really not many points in which the defending king has a choice, so it's pretty easy to master after the initial learning phase. maybe an hour or two of continuous drilling.

Here's an example I blitzed against Chessmaster, moving immediately after it did. It's not the fastest way to do it, but it works.


[White "wormwood"]
[Black "Chessmaster 9000"]
[Result "1-0"]
[Setup "1"]
[FEN "8/3B4/8/5K2/3k4/8/8/5N2 w - - 0 1"]
1.Ng3 Ke3 2.Bc6 Kd4 3.Kf4 Kc5 4.Bf3 Kd4 5.Nf5+ Kc3 6.Ke3 Kc2 7.Nd4+ Kc3 8.Be2 Kb4 9.Ne6 Ka3 10.Kd3 Kb3 11.Nc5+ Kb4 12.Kd4 Ka3 13.Kc3 Ka2 14.Bd1 Kb1 15.Nd3 Ka2 16.Bc2 Ka3 17.Nc5 Ka2 18.Nb3 Ka3 19.Bb1 Ka4 20.Nd4 Ka5 21.Kc4 Kb6 22.Nb5 Kb7 23.Bf5 Kc6 24.Be6 Kb6 25.Bd5 Ka5 26.Kc5 Ka4 27.Bc4 Ka5 28.Bb3 Ka6 29.Nd6 Ka5 30.Nb7+ Ka6 31.Kc6 Ka7 32.Bc4 Kb8 33.Nd6 Ka7 34.Kc7 Ka8 35.Bb5 Ka7 36.Nc8+ Ka8 37.Bc6# 1-0