Chess Variants/Checkless Chess

Introduction
Checkless chess is a variant that forbids players form delivering check.

History
It is not known where checkless chess came from, but the variant dates from the mid-19th century, and it also often used in fairy chess problems.

Rules
Checkless chess is played mostly like the original game, with one difference - moves that deliver check to the enemy king are forbidden unless they deliver immediate checkmate.

There are several other optional rules:


 * If a player is not in check but their only legal moves deliver check, that is stalemate and the game is drawn.
 * A check is considered checkmate if the only legal responses are cross-checks.
 * Checks are permitted of they are part of a series resulting in forced mate.

Sub-variants

 * Absolute checkless chess bars pieces from moving over squares where they would give check.