Chess Variants/Progressive Chess

Introduction
Progressive Chess is a variant developed for speedy play by a slow medium such as correspondence mail.

History
It is not known where progressive chess came from, but as already stated it is a popular variant to play by correspondence because of the small number of moves in a typical game.

Rules
Progressive chess is played like the standard game, with one key difference - rather than making one move per turn, the players take turns making progressively longer sequences of moves. After White makes the first move, Black makes two moves, then White makes three moves, then Black four and so on until the end of the game.

There are two main rulesets for progressive chess: the Italian rules and the Scottish rules. The two rulesets share the following rules in common:


 * If a player is in check, they must escape the check with their first move. If this is not possible, they are in checkmate and they have lost.
 * An en passant capture is allowed if the pawn being captured moved two squares, but no further, at some point during the last turn. The capture must be made as the first move in a sequence.
 * If ten consecutive turns are played without a capture or a pawn move, the game ends in a draw unless checkmate can be forced by one of the players (This is the progressive equivalent of the fifty-move rule).
 * If either player has no legal move at the start of their turn, but is not in check, the game ends in stalemate.

The Italian and Scottish rulesets differ on what happens if a player places their opponent in check as part of their turn:


 * Under the Scottish rules, as soon as the check is delivered that player's turn is cut short, and the next player takes their turn.
 * Under the Italian rules, only the last move of a sequence may be used to deliver check. Any check before then is forbidden.

Sub-variants

 * English progressive chess: No piece may be moved twice in one turn unless every other piece of that player on the board has also been moved.
 * Progressive take-all: A combination of progressive chess and losing chess (see that variant's page for more information).
 * Logical progressive chess: There is no castling, pawn double-step or en passant captures.