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King's Guard Chess

Introduction

My design aims with this variant were threefold:
  • the game could be played using standard equipment;
  • changes to FIDE rules  should be few;
  • it should be difficult for a computer to play well.
The first has certainly been achieved, as has, in my opinion, the second. The achievement of the third is, however, still open to question.

Setup

The starting arrangement of Pawns and Pieces is exactly the same as that found in FIDE chess but with the Pawns adopting the King's (Guard's) movement, thus forming the King's Guard of this variant's name.

This initial set-up is shown in the top image on the right, where the Guard icon has been used for the Pawns.   This is to emphasise the Pawn's enhanced movement in this variant.

In over-the-board play the Pawns can still be used though their movement and capturing abilities will be as described below.

Rules

Unless otherwise stated FIDE rules apply.

All pieces, except the Pawn, move as in FIDE chess. 
Pawns move one square in any direction, like a King or Guard.
There is no initial double-move for a Pawn and thus no en-passant capture.
There is no castling.

Pawns do promote on entering the far most rank.

Only the Pawns may capture, and then only if assisted by a non-Pawn. 

A Piece provides an assist by attacking the square containing the enemy to be captured. 

Pawns may not assist.  Kings, Queens, Rooks, Knights and Bishops assist; Pawns capture.

This assisted capture is illustrated in the lower image on the right.
  • Knight c2 can only move to e3, a1, or a3.  It also attacks d4 and b4 thus providing the Pawn on c3 with the assists needed to capture either the Pawn on b4 or the Rook on d4.  The Knight on b3 cannot be captured as no assist is available.
  • King on e8 is safe from capture despite the proximity of the Pawns on d7 and e7 since no assist is available.   Pawns cannot assist and the Bishop on c6 is blocked from attacking e8 by the Pawn on d7.
  • Pawn f7 could capture Pawn e7 since the King on e8 provides the required assist.
The object of the game is to capture the enemy King.

A side loses if:
  • its King is captured
  • it has no Pawns in play (all either captured or promoted)
  • it cannot make a legal move (stalemate).
The loss conditions for a player are assessed at the start of a player's turn. Thus if Black captures White's last Pawn on the first rank with Black's last Pawn which then promotes, both players are left Pawn-less. White, however loses since it is now White's turn and White against whom the loss conditions are applied.

White would also lose if Black's last Pawn had been promoted but had also captured White's King or in being promoted had rendered White unable to move (stalemate).

Notes

Assisted Capture

There are variants that use methods of capture other than replacement and there are variants where a piece's ability to capture is restricted or non-existant; but I have not found one where capturing consistently requires the interaction of two different classes of piece.  Perhaps I just need to keep looking.  The closest I can find is the method used in Archimedes Chess where a piece is captured if it is attacked by two or more enemy pieces.

Piece Values and Computers

I am unclear how to assign values to individual pieces.  My Zillions implementation gives these relative values:

Pawn
1.0
Knight
2.0
Bishop
2.5
Rook
4.0
Queen
6.5








This seems to over-value the assisting pieces and under-value the Pawn.  My initial guess would be that all pieces are of roughly equal value.

I hope, but cannot prove, that the unusual (I don't dare say unique) rule of capture with the need for cooperation  between pieces will render current chess-playing algorithms at least partially ineffective.


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By Graeme C Neatham.
Web page created: 2008-06-12. Web page last updated: 2008-06-12