Changes

'''Unmake Move''' is a function inside a chess program to update the internal [[Chess Position|chess position]] and its [[Board Representation|Board representation]] as well as associated or dependent state variables and data by a move unmade on the internal board. In unmake move, reversible aspects of a position can be [[Incremental Updates|incrementally updated]] by the [https://en.wikipedia.org/wiki/Inverse_function inverse] or [https://en.wikipedia.org/wiki/Involution_%28mathematics%29 own inverse] operation of [[Make Move]]. Irreversible aspects of a position, such as [[En passant|ep state]], [[Castling rightsRights|castling rights]] and the [[Halfmove Clock|halfmove clock]] are either restored from a [[Stack|stack]] ([https://en.wikipedia.org/wiki/LIFO_%28computing%29 LIFO]), or simply kept in arrays indexed by current search or game [[Ply|ply]]. Alternatively, one may capacitate the move with all the necessary information to recover those irreversible aspects of a position as well.