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Game: Forced Chess
 
Created by Karl Scherer, 2010-05-29
version 1.0
4 variants

Checkmate
Solitaire

download 14 K
 
 

Object: Construct sequences of forced chess moves.

You are asked to create long sequences of forced chess moves.
'forced' here means that the player (White or Black) has only one move he/she can play.

The longest sequence depends on the additional conditions you may demand to be fulfilled.

Variant 1 shows the longest known forced sequence for a 'legal' chess position.
It runs for 18 half-moves (also called plies), hence both player have only one move available while they are playing 9 moves each!
Can you find a longer sequence?
The position given here is 'legal', which means the setup can be reached from the standard chess start-setup using only legal chess moves.
(Can you find such a sequence leading to the given position?)

Variant 2 also shows a legal position, but the forced sequence (running for 14 plies) is not quite as long as the first variant.
Variant 3 (using 11 plies) is the best known legal position without promoted pieces.

Variant 4 is called 'freeplay'. It shows the starting position. Here you can create your own designs for chess positions with long forced sequences.
Sample chess pieces are given at the right border.
This makes it easier to set uo your own chess position.
Use CTRL+C+mouseclick to 'copy' a piece from the sample list and use CTRL+V+mouseclick to paste the selected piece onto the board.

Here are a few problems you might want to solve:
What is the longest forced sequence with a legal position does not use promoted pieces?
Here you can use only the standard piece set.

What is the longest forced sequence where the position does not have to be legal (you can use as many rooks, queens etc as you like)?

Here is how you check that only one move is available in a position:
Select Play/ChooseSide and then activate both 'White' and 'Black'.
Click F7 and keep it pressed. Blue markers show the pieces you can move.
There should be only one marker.
Now click the marked piece.
The move should be executed immediately.
This means that the system could only find one target position for this piece.
Hence there was only one move available for the current player.


The problem of long sequences of forced chess moves was published in the Journal Of Recreational Mathematic 9:2, 1975-1976, pp130-131.
The position in variant 1 (world record, 18 plies) was found by Karl Scherer.
The position in variant 2 (14 plies) was found by Scott Nelson.
Both positions were published in the JORM journal.
The variant 3 (using 11 plies) is based on Scott Nelson's effort and was found by the author.

 

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Forced Chess

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