Retro Chess

Introduction

Retro Chess is chess played backwards. Each move is the reverse of a normal chess move. This game is one implementation of the ideas in the Retro Chess Challenge (see the Related items).

Setup

The game begins with just the kings on the board: the White king at e6, and the Black king at e3.

Pieces

The game uses the standard set of chess pieces. All of them start off the board, except for the kings.

Rules

The game is divided into two phases, named Phase I and Phase II.

In Phase I, Black goes first. Each turn is either an unmove or an uncapture.

An unmove is the reverse of a normal chess move. For most pieces, an unmove looks like a regular move. However, when a pawn unmoves, it goes backwards (towards its initial position). For example, in the diagrams below, White unmoves a pawn, and then Black unmoves a rook.

 White: P e6-e5 => Black: r b2-f2 =>

An uncapture is the reverse of a normal capturing move. The uncapturing piece moves away from its square, and leaves an enemy piece behind on that square. For example, in the diagrams below, Black's king uncaptures a White bishop, and then White's bishop uncaptures a Black knight.

 Black: k e7-f7; B-e7 => White: B e7-c5; n-e7 =>

Note: No extra copies of a piece are allowed during uncapturing (i.e. a 3rd rook, a 2nd queen, etc.).

Phase I ends when all 32 pieces are on the board. At that point, the two players switch colors. Then Phase II begins. During Phase II, only unmoves are made (no uncaptures).

The goal is to get all 16 pieces back to their traditional opening setup. Whoever achieves that first wins. If neither side can make any more progress towards the goal, then whoever has more points wins. Points are awarded for pieces that have reached the goal: 1 point for each pawn, and 2 points for each of the other pieces.

There is no check or checkmate in Retro Chess. But there is "kcehc" (pronounced "ketch"). If a player's unmove (or uncapture) places himself in check, then his opponent has to undo the check with his next unmove. For example, in the diagrams below, Black's king uncaptures a White queen, placing White in kcehc. White gets out of kcehc by moving the queen away.

 Black: k c5-b6; Q-c6 (kcehc) => White: Q c5-g5 =>

When read backwards, the diagrams yield these moves: Q g5-c5 (check), KxQ. The game should always follow the rules of a standard chess game if the unmoves are undone.

In Retro Chess, it is illegal to make a move that places one's opponent in check. For example, in the diagrams below, White cannot move the rook as shown, because it would place Black in check.

 White: R a5-f5 =>

When read backwards, the diagrams reveal an illegal situation: it is White's turn to move, but Black is in check.

Every position in a game of Retro Chess should be a legal position that could be reached by a series of legal moves, starting from the initial position of FIDE Chess. If a move would result in an impossible position, then the move is not allowed. For example, in the diagram below, Black cannot uncapture a White pawn at h3, because the resulting position is impossible: White could not have pawns at g2, h2, and h3.

 Black: n h3-f4; P-h3 =>

Pawn promotion is not allowed in Retro Chess, since the pawns always move backwards towards their home squares. If a pawn is on the 4th rank, it can unmove two squares to the 2nd rank (which freezes the pawn for the rest of the game). A piece on the 8th rank (not a king) can be unpromoted to a pawn on the 7th rank.

Notes

The mid-game color switch is needed because without it, neither player would have an incentive to uncapture any enemy pieces.

Optionally, style points can be awarded for special unmoves, such as uncastling and un passant.

The author was inspired by the diagrams and discussions at the Retro Chess Challenge page of the Chess Variants web site.

Playing Tips

In Phase I, plan ahead. Uncapture pieces as close to their home squares as possible, because in Phase II, you will own those pieces. Uncapture a piece whenever possible, because if one player finishes all 16 uncaptures before the other, then the player who's finished can make extra unmoves before Phase II.

In Phase I, when unmoving or uncapturing from the 8th rank, it can be advantageous (and fun) to unpromote a pawn. It will take many unmoves to bring that pawn home, but that will be your opponent's problem in Phase II.

Computer Play

You can also play Retro Chess by email, using the web-based Play by Mail system on this site.

Written by Mike Smolowitz.

WWW page created on August 19, 2013.

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