Overloading

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Overloading is a chess tactic where a piece has more than one exclusive defending obligation. For instance, if the defending piece is member of two or more balanced defend and attack sets (equal number of attacks and defends) of their respective critical squares, the piece is likely overloaded, except for defending sliding pieces with both squares connected by a single move. Critical squares, attacked by the opponent, are either occupied by pieces from the defenders side, and/or otherwise mate threatening squares around the king or the backrank.

Despite tactics is the domain of search, and static evaluation of overloading pieces seems complicated considering tactical interactions and issues like pieces en prise or hanging, discovered attacks, checks, pins, Zwischenzug and counter attacks, some programs statically determine overloading pieces and other tactical motives for counting all kinds of obligations to consider their balance in nonlinear evaluation terms and/or controlling the search, quiescence search and their selectivity.

=Sample= Here, in the left diagram, White to move wins a piece with Bxd3, since the black d7 rook is overloaded defending d3 and b7. However in the right position it does not work as intended, since Black has the Zwischenzug 1... Bxf3, which also demonstrates the difficulty to evaluate chess tactics statically.

=See also=
 * Attack and Defend Maps
 * Deflection
 * SEE - The Swap Algorithm
 * Square Attacked By
 * Static Exchange Evaluation
 * Undermining

=External Links=
 * Overloading (chess) from Wikipedia
 * Chess Corner - Chess Tutorial - Overloading
 * Chess overloading from chessguru.net
 * Passport - Cross-Collateral (1975), YouTube Video
 * lineup: Klaus Doldinger, Curt Cress, Wolfgang Schmid, Kristian Schultze

=References= Up one Level