|Q:||What is Tsumeshogi?|
||Tsumeshogi is a form of puzzle based on the rules of shogi.
A Tsumeshogi problem is posed in the form of a shogi diagram.
The Attacker ["Semekata"] plays first from the bottom.
The Defender ["Gyokugata"] plays from the top.
Normally, the Attacker's king is not shown.
Rules of Tsumeshogi
- The Attacker must mate with a continuous series of checks.
- Both Attacker and Defender must play the best moves.
- The Defender may use any piece that is not shown.
- The Defender may not resort to futile interpositions.
- Otherwise, the normal rules of shogi apply.
||Why does the Attacker have to give check every move?|
|A:||To those familiar with chess problems, this rule may seem odd.
But actually, it makes good sense. The thing to remember is that in a game situation,
the Attacker's King is exposed to danger the instant he stops giving check.|
||What is meant by "the best moves"?
|A:||The "best moves" are defined as follows:
A variation that ends with pieces remaining in Attacker's hand is known as "koma-amari".
- The Attacker strives to mate in the smallest number of moves, using as few as possible of his pieces in hand.
- The Defender strives to avoid mate for as long as possible, AND force the Attacker to exhaust all pieces in hand.
A "koma-amari" variation is never the correct solution.
||Can the Defender drop a third Bishop?
No. The Defender is considered to have in hand all pieces from the original set of 39
(40 minus Attacker's king) that are not shown on the board or in Attacker's hand.
This is sometimes part of the problem.
This amusing geometrical problem was composed by Hatasu Ito (7-dan).
After the initial moves 1 S2i K1i 2 S3h, Defender could avoid mate if only he could drop
a Bishop or Silver on 3i. Unfortunately (for him), both Bishops and all four
Silvers are already accounted for...
||What is a "futile interposition"?
||Defender may block a check by Rook, Bishop, or Lance by moving a piece or, as stated above,
by dropping any piece not already shown. This is known as an "interposition." An
interposition is considered futile if the Attacker can simply capture the interposed
piece without otherwise changing the solution. Futile interpositions are disallowed.
But watch out, sometimes there's a trick...
|Futile Interposition||Tricky Escape|
||Defender is in check by the Lance. Interposition on
2b or 2c is futile.
1... K1a is Defender's only move, after which
he will be mated by 2 L2b+.
||Same position, minus one pawn. 1... K1b 2 L2c+ K2a 3 G2b is mate, but...
1... P2c (!) avoids mate entirely.
2 L2c= K1b 3 L2b+ K1c and the king wiggles out.
Worse, 2 L2c+ is not even check.
The pawn drop bears critically on the solution and thus is not futile.
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98 September 13
davin [at] shogi [dot] net