The Java theme

The Java theme, mostly seen in two-move problems, exemplifies the idea of dual avoidance. The latter term means that after a certain black defence, White apparently has a choice of two mating moves (a dual), but one must be discarded for a subtle reason. This basic effect takes a special form in the Java theme, which focuses on how two white line-pieces control the flight-squares next to the black king. A black move, which seems to permit a dual, cuts off a white line that guards a flight; in the mating response, White must avoid closing another white line that targets the same square, as that would allow the king to escape. The theme is named after the island where an early exponent, the Danish composer Harry Tuxen, was residing in the 1930s.

Let’s start with a clear-cut and economical example. A good key 1.Sxd5! gives the black king access to h5 and threatens 2.Qf7. White’s thematic line-pieces are the queen and bishop, both of which control the f6-flight. Black’s bishop has two defences against the threat, and either will activate the white rook along the fifth rank. After 1…Bf2, the knight seems able to mate in two ways (by opening the R + S indirect battery), but since the black bishop has shut off the queen on the f-file, 2.Se7? fails to 2…Kf6! when Black exploits the knight’s interference with the d8-bishop; therefore only 2.Sf4 works. Similarly, 1…Be7 – shutting off the white bishop – cannot be met by 2.Sf4? which interferes with the queen and enables 2…Kf6!; so the unique mate is 2.Sxe7. The theme normally involves a reciprocal aspect as shown in this problem, i.e. two white lines alternate at being closed by Black and left open by White. Subsidiary variations are 1…Kh5 2.Qf5 and 1…h5 2.Qf6.

Here the thematic play after the key is augmented by two important tries that act like a prelude. Moreover, the main defences by the f6-knight are given set mates, 1…Se4 2.Qxe4 and 1…Sd5 2.Qxd5, that will be changed. Both try-moves guard c4 and free the e5-knight to mate, but there is only one threat in each case. 1.Ba6? (2.Sc6 not 2.Sf3?) is refuted by 1…Se4!, which cuts off the queen and creates a flight on d5; and 1.Qc2? (2.Sf3 not 2.Sc6?) is defeated by 1…Sd5! which cuts off the bishop and creates a flight on e4. The key 1.b3! also guards c4 but grants a flight on c3, so no mate is threatened by the e5-knight; instead the threat is 2.Qb2. When the f6-knight defends, the set mates don’t work anymore, but the white B + S battery on the long diagonal is unmasked and this leads to the Java variations. 1…Se4 shuts off the queen, 2.Sf3 – not 2.Sc6? interfering with the bishop, 2…Kd5! 1…Sd5 shuts off the bishop, 2.Sc6 – not 2.Sf3? interfering with the queen, 2…Ke4! Also, 1…Kc3 2.Qb2 and 1…Sa2/Se2 2.Rxd3. Note how the following moves change their functions across the three phases: 1…Se4/Sd5 served as refutations to the tries, but become normal defences post-key; 2.Sc6/Sf3 served as threats after the tries, but become variation mates post-key.

In a cyclic Java, three white line-pieces observe various flight-squares, and when a black piece closes these lines of guard one by one, White must be careful not to shut either of the other two lines. The demonstration above begins with 1.Bc6!; now White’s bishop and rooks are each controlling two of the three flights on g2, h2, and h1. The threat is 2.Rg2, which the g3-knight can parry by blocking any of the three white line-pieces. When this black piece moves, White seems to have three possible knight mates, since e2 is left unprotected while the g4-pawn is liable to be pinned. But only one mate is viable after each defence, in view of the potential interferences. 1…Se2 2.Sxe2, not 2.Sf3? Kg2!, 2.Sh3? Kh2!; 1…Se4 2.Sf3, not 2.Sh3? Kh1!, 2.Se2? Kg2!; and 1…Sh5 2.Sh3, not 2.Se2? Kh2!, 2.Sf3? Kh1! Black has one other defence, 1…Rxh6 which enables 2.Qa7 – this explains why the key-bishop must land on c6, to prospectively close the sixth rank. Earlier compositions employing the same matrix exist (see P1065641, P1024520), so arguably this problem is anticipated. However, this is a perfect 12-piece setting with no distracting variations that duplicate the thematic knight mates.

This two-mover blends the line strategies of Java with a complex form of changed play. In two set variations, Black self-blocks flights on c6 and b6 controlled by the c1-rook and g1-bishop, thereby allowing the e2-knight to interfere with these pieces with impunity: 1…Sc6 [a] 2.Sc3 [A] and 1…axb6 [b] 2.Sd4 [B]. The thematic key 1.Qg6! covers the same flights immediately but also self-pins the e2-knight, which is thus unable to mate. White’s threat of 2.Rc5 is thwarted by the two defences seen in the set play, but they result in changed mates: 1…Sc6 [a] 2.Qxc6 and 1…axb6 [b] 2.Qxb6. Black can also defend by cutting off the c1-rook or g1-bishop, and this produces the dual avoidance variations. 1…Bc2 commits the error of unpinning the knight by interposition; then White must avoid 2.Sd4? Kc5! and so chooses 2.Sc3 [A]. 1…f2 also interposes on the pin-line and releases the knight; now not 2.Sc3? Kc5! but 2.Sd4 [B] is necessary. These knight mates occurred in the set play against another pair of black moves, so the mates have been transferred to new defences. This mix of changed mates (after [a] and [b] defences) and mate transference (for mating moves [A] and [B]) is called the Rukhlis theme. Here it’s impressively combined with Java interference play, not to mention the appealing self-pin + unpin effects. There’s by-play in 1…f4 2.Qd3 and 1…Sd7 2.Qc6.