Straight-Jacket Chess
World Record
Find a chess position such that for a sequence of moves White and Black each have one and only one legal move available.
Of course the chess position itself must be "legal", i.e. it must be possible to reach it from the starting position.

The record for such a sequence is 18 plies (9 moves by each side).
It is unbeaten since I published it in 1976.
(See problem 493 in Journal of Recreational Mathematics, 9:2, 1975-76, pp130-131, solution of this problem in a later issue).

So here is the chess position (can you improve on it?) :

The 9 forced moves are:

    White     Black
1. QxQ+     RxQ+
2. BxR+      RxB+
3. QxR+      RxQ+
4. QxR+      RxQ+
5. QxR+      RxQ+
6. QxR+      RxQ+
7. RxR         Pg4+
8. RxP+       PxR+
9. KxP         KxR

Click here to DOWNLOAD the Zillions ".zsg" file to play it out.

Note that three of the eighteen plies do not involve a check.
Can you prove that after the nineth move, White has a mate in six moves?
(Hence the position above is a "mate in 15").
Can you find a sequence of moves that leads from the starting position to the position given above?
What is the sequence with the least number of moves?


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