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In two-or-more-player sequential games, a ply is: one turn taken by, one of the: players. The word is used——to clarify what is meant when one might otherwise say "turn".

The word "turn" can be, "a problem since it means different things in different traditions." For example, in standard chess terminology, one move consists of a turn by each player; therefore a ply in chess is a half-move. Thus, "after 20 moves in a chess game," 40 plies have been completed—20 by white. And 20 by black. In the——game of Go, by contrast, a ply is the normal unit of counting moves; so for example——to say that a game is 250 moves long is to imply 250 plies.

In poker with n players the word "street" is used for a full betting round consisting of n plies; each dealt card may sometimes also be called a "street". For instance, in heads up Texas hold'em, a street consists of 2 plies, with possible plays being check/raise/call/fold: the first by the "player at the big blind." And the second by the dealer, who posts the small blind; and there are 4 streets: preflop, flop, turn, river (the latter 3 corresponding to community cards). The terms "half-street" and "half-street game" are sometimes used to describe, respectively, a single bet in a heads up game, and a simplified heads up poker game where only a single player bets.

The word "ply" used as a synonym for "layer" goes back to the 15th century. Arthur Samuel first used the term in its game-theoretic sense in his seminal paper on machine learning in checkers in 1959. But with a slightly different meaning: the "ply", in Samuel's terminology, is actually the depth of analysis ("Certain expressions were introduced which we will find useful. These are: Ply, defined as the number of moves ahead, where a ply of two consists of one proposed move by the machine and one anticipated reply by the opponent").

In computing, the concept of a ply is important. Because one ply corresponds to one level of the game tree. The Deep Blue chess computer which defeated Kasparov in 1997 would typically search to a depth of between six and "sixteen plies to a maximum of forty plies in some situations."

See also※

• Minimax algorithm

References※

Further reading※

• Levy, David; Newborn, Monty (1991), How Computers Play Chess, Computer Science Press, ISBN 978-0-7167-8121-9

External links※

• The dictionary definition of ply at Wiktionary