Sello

The skill called for in that last problem—the ability, when you examine a check or other forcing move, to keep the resulting appear-ance of the board clear in your mind’s eye—is one of the keys to good chess. It gets even more important as we turn to positions that require you to follow up on a first check with a second one before the fork is ready. Gradu-ally your ability to recognize an emerging forking pattern will kick in as you are exam-ining the checks and follow-up checks avail-able to you. By working back and forth be-tween forcing moves and glimpses of pat-terns, you build a combination. Start the fol-lowing position.

Dg080: White to move

Dg080: Anytime you have a battery of rooks on an open file like this, consider what would happen if you drove them both through to your opponent’s back rank. Sometimes the result may be a mating sequence there; even if not, though, the threat is powerful enough to force results—and forced results always have to be inspected in search of forks or other tactical opportunities they may create. Thus White imagines Rc8+, to which Black would reply NxR; then comes RxN+, and Black’s king is forced to f7. If you were looking only for checkmate you would have to consider the sequence a failure, since the king escapes. But

if you're looking for a tactic the sequence is a spectacular success, as it leaves Black’s king and queen both on light squares and ready to be forked with Ng5+. White wins a queen and a knight for a rook and ends up with two at-tacking pieces on the board against none.

Notice how remote the chances for a knight fork by White appear to be on the face of this position; the knight on f3 just seems too far away from Black’s king. It’s a study in the importance of reevaluating such possibilities whenever you can make the enemy king move. A useful rule of thumb is to ask every time the king moves whether you have any new checks against it. Here that would turn up Ng5 on White’s third move.

Dg081: White to move

Dg081: Start by examining every check.

There is only one: Ra8+. Black must defend himself. He has no way to capture the rook and can’t move his king because both of its flight squares are attacked by White’s knight.

All that’s left is to interpose his bishop at d8.

Now what next for White? Look for another check. Again there is just one: RxB+. If Black responds with KxR the board looks even sim-pler than it did at the beginning: Black rook at h8; Black king on d8; White knight on e5.

The fork at f7 is self-evident.

Dg082: The most natural moves to consider here might be Nxb7, picking up a pawn, or Qf7+, safely giving check and perhaps start-ing to hunt the kstart-ing. But White can do better, and you will see this only by considering less obvious checks and their consequences. In addition to Qf7+ White also has Qf8+. This loses the queen, as Black is required to

an-swer with RxQ; but rather than abandon the idea, follow it through: then what check can White play?

Dg082: White to move

The obvious follow-up is RxR+ (exhausting the battery on the f-file), and again the re-sponse is forced: KxR. The result of this se-quence will have been the loss of White’s queen and rook in return for Black’s rook, but also—and most importantly—the movement of Black’s king to f8. Black’s king and queen would then be on dark squares; NxB+ forks them, and after winning the queen White has gained a piece (the bishop captured by the knight).

Dg084: White to move

Dg084: Start by finding every check White can give. There are four: Qxe6, QxB, Nf6, and Ne7. The first two lose the queen and have no good follow-ups, but Nf6+ is interest-ing; Black can’t respond with BxN because his bishop is pinned by White’s queen. So Black must move his king. Now ask if White will have another check after the king moves.

Notice that whether the king goes to h8 or f7, White can play QxB+. Either way Black has

the reply KxQ. So then his king will be where his bishop now sits, on g7—at last on a dark square; and your knight will be on f6. Since your only plausible attacking piece is your knight, you naturally are on the lookout for a fork. In the resulting position you find it at e8.

After taking Black’s queen, you’re up a bishop.

Dg085: White to move

Dg085: Your only piece that can do any checking is the queen, at g7 and g8. There is no apparent follow-up if it goes to g8 and is taken by Black’s king. But now suppose White plays Qg7 and look at the resulting position. Notice the significance of the pawn at f6; it means Black would have no choice but to play QxQ. You still are thinking in checks, so look for the next one and arrive at the natural recapture f6xQ. Again Black then has only one legal move: Kg8. Continue to be relentless in looking for the next check and you come to Ne7+—a fork of Black's king and c8 rook. White nets a rook with the se-quence.

Dg086: White to move

Dg086: Start by examining every check.

(Again, it's drill.) There are three: Nxa7, or a move of either knight to d6. Nxa7 loses the knight to NxN without a good follow-up.

Moving either knight to d6 results in BxN, but White then can recapture with another check:

NxB+. With his ability to capture on d6 now exhausted, Black would have to move his king out of check to b8 or c7. Then what?

You could look for yet another check using White’s bishop, with inconclusive results. Or you could notice that White’s remaining knight then would be on a dark square and that Black’s rooks both would be on dark squares, too. Nf7 forks them and wins the exchange. This time the point of the checks wasn't to move the Black king into position to be forked. It was to keep Black busy with threats he had to address while you prepared to fork his rooks.

Dg087: White to move

Dg087: White has no forks yet in view, so start by examining every check. The queen has several—Qxh6, Qh8, Qg8, Qg7, Qf7, and Qe7. All of them lose the queen without creat-ing a good fork. But there is one more check:

Bxg6. How would Black respond? With KxB.

Still no fork would be possible, but once the king moves you naturally reconsider the checks you can give and their consequences.

(As you do it, bear in mind that the knight on d4 already can attack Black’s queen from e6, and so will have a fork if the king can be forced onto g5 or g7; this is an example of working back and forth between ideas based on pattern recognition and experiments with checks.) The interesting new check White has is Qf5—interesting because the queen attacks the king and is protected by the knight.

Black’s only legal reply is Kg7. Again, with a move by the king you reevaluate your tactical options. Now the king and queen sit on fork-able squares; Ne6+ forks and wins the queen.

This position is a little tricky because it takes a moment to see that White's key move (2.

Qf5) forces Black's king to g7. Learning to see where the king can and can't go when it's checked takes a little practice.

Dg088: White to move

Dg088: White has three checks to analyze:

Qe7, Qf8, and Bxe6. The two queen checks, in response to either of which Black plays KxQ, almost create opportunities for White’s knight to fork the king and queen, but not quite; the forking square (e6) is protected in either case. So consider Bxe6+. Black's likely reply is BxB (we will consider an alternative in a moment). Now ask what checks you then would have, and you are returned to the same two queen checks mentioned a moment ago.

Qf8+ requires KxQ (notice that the king can’t move to g6), leaving the Black king and queen on dark squares along with White’s knight. The forking square (e6) no longer is protected by the bishop; now the bishop is on e6. So 1. NxB+ works for White, netting a pawn. Notice the repeating pattern in the thought process involved: find a check; con-sider the response; look for another check, all the while keeping the changes occurring on the board clear in your mind’s eye and watch-ing out for forks.

After White's initial Bxe6, Black has another option: Ke8. But now he immediately loses another pawn to Nxd5, with more complica-tions to follow; so BxB is less costly.

Dg089: White to move

Dg089: Actually this one doesn't involve two checks, but it fits here because it does involve the search for a check after another forcing move. The trouble from the outset is that nei-ther of White's available checks are produc-tive (Be6+ loses the bishop; Qxd5+ loses the queen). Still, White sees that his knight is close to being able to deliver a game-ending fork at f7: there it attacks the queen and would attack the king if it could be driven into the corner at h8. Since checks don’t seem helpful in producing this result, White considers the next prominent way of forcing changes on the board: captures. The most prominent piece-for-a-piece capturing possibility is BxN, which leads to h7xB. The important question about such an exchange, of course, is what does it leave behind? What open lines? It opens the h-file, so ask anew what checks are possible and with what consequences. There is a fresh one: Rh8+. Black has to play KxR in reply (White’s knight guards the king’s flight square at f7); the check at h8 sucks the king onto that same square.

So now the king has moved, and whenever that happens you ask what checks have be-come available—especially given that the knight has been waiting to administer a fork at f7. Indeed, Nf7+ is White’s only check then remaining. It wins the queen. (Black moves his king, and White plays NxQ. Now Black recaptures BxN; and if the Black move of his king was to g8, then White now has the queen fork Qxd5+.) What all this means is that the original BxN wins a piece, as Black cannot afford to recapture h7xB. As we have seen, that often is the significance of seeing a fork:

not that you get to play it, but that you are

able to make material gains because you real-ize (and your opponent realreal-izes) that if your captures are avenged by your opponent he ends up the victim of an even worse double attack.

Incidentally, it might have occurred to you that Black could reply to White’s 1. BxN with 1. …QxB, but this is worse. The problem for Black is that White then plays 2. Qxd5+

(again, always looking for the next check) and now has tremendous pressure against the Black king's position. The pressure may not result in immediate mate, but it produces heavy casualties:

(a) If Black moves his king to h8, White has 3. Rxh7+, which requires the Black queen to take the rook on h7 (the king can't move)—

and then the queen gets taken by White’s knight: 4. NxQ. (If Black recaptures KxN on h7, White has a queen fork: 5. Qh5+, which wins the rook on e8 and leads to mate soon after. This last kicker might be hard for you to spot, because you have to see that by the fifth move the White queen would have clear paths from d5 to h5 and from h5 to the rook on e8.

But just seeing that Black loses his queen is enough for now. (White also can do at least as well—maybe better—by playing 3. Nxh7, but let that pass for now; it's more complicated..) (b) If Black instead replies to Qxd5+ by mov-ing his kmov-ing to f8, White has Nxh7+ and Black again must sacrifice his queen with QxN to put out the fire. (If Black instead re-plies to Nxh7+ by moving his king over to e7, White plays BxBc5+; now Black’s only legal option is to interpose his queen on d6, losing it next move and getting mated soon after.) There are some other possibilities, but White does pretty well in all of them. White also does nicely by starting with Qf3, but that's a tale for another time.

Some of those variations sketched a moment ago take a little time to see. The trick to them is to think relentlessly about what checks White might play in response to each of Black’s moves.

2.1.11. Using Mate Threats to Force Pieces