Fork (chess)

In chess, a fork is a tactic whereby a single piece makes two or more direct attacks simultaneously. Most commonly two pieces are threatened, which is also sometimes called a double attack. The attacker usually aims to gain material by capturing one of the opponent's pieces. The defender often finds it difficult to counter two or more threats in a single move. The attacking piece is called the forking piece; the pieces attacked are said to be forked. A piece that is defended can still said to be forked if the forking piece has a lower value.

Besides attacking pieces, a target of a fork can be a direct mating threat (for example, attacking an unprotected knight while simultaneously setting up a battery of queen and bishop to threaten mate). Or a target can be an implied threat (for example, a knight may attack an unprotected piece while simultaneously threaten to fork queen and rook).

Forks are often used as part of a combination which may involve other types of chess tactics as well.

Fork

As a piece of cutlery or kitchenware, a fork is a tool consisting of a handle with several narrow tines on one end. The fork is a primarily Western utensil, whereas in East Asia chopsticks have been more prevalent. Today, forks are increasingly available throughout East Asia. The usually metal utensil is used to lift food to the mouth or to hold ingredients in place while they are being cut by a knife. Food can be lifted either by spearing it on the tines, or by holding it on top of the tines, which are often curved slightly. A fork is shaped in the form of a trident but curved at the joint of the handle to the points.

Early history of forks is obscure, as a kitchen and dining utensil it's generally believed to have originated in the Roman Empire, as proved by archaeological evidences. The personal table fork most likely originated in the Eastern Roman, or Byzantine, Empire. Its use spread to what is now the Middle East during the first millennium CE and then spread into southern Europe during the second millennium. It did not become common in northern Europe until the 18th century and was not common in North America until the 19th century.

Intersection (road)

An intersection is the junction at-grade (that is to say, on the same level) of two or more roads either meeting or crossing. An intersection may be three-way (a T junction or Y junction – the latter also known as a fork if approached from the stem of the Y), four-way (often in the form of a crossroads), or have five (a 5-points) or more arms. Busy intersections are often controlled by traffic lights and/or a roundabout.

This article primarily reflects practice in jurisdictions where vehicles are driven on the right. If not otherwise specified, "right" and "left" can be reversed to reflect jurisdictions where vehicles are driven on the left.

Types of intersections

Road segments

One way to classify intersections is by the number of road segments (arms) that are involved.

Fork (system call)

In computing, particularly in the context of the Unix operating system and its workalikes, fork is an operation whereby a process creates a copy of itself. It is usually a system call, implemented in the kernel. Fork is the primary (and historically, only) method of process creation on Unix-like operating systems.

Overview

In multitasking operating systems, processes (running programs) need a way to create new processes, e.g. to run other programs. Fork and its variants are typically the only way of doing so in Unix-like systems. For a process to start the execution of a different program, it first forks to create a copy of itself. Then, the copy, called the "child process", calls the exec system call to overlay itself with the other program: it ceases execution of its former program in favor of the other.

In Unix systems equipped with virtual memory support (practically all modern variants), the fork operation creates a separate address space for the child. The child process has an exact copy of all the memory segments of the parent process, though if copy-on-write semantics are implemented, the physical memory need not be actually copied. Instead, virtual memory pages in both processes may refer to the same pages of physical memory until one of them writes to such a page: then it is copied. This optimization is important in the common case where fork is used in conjunction with exec to execute a new program: typically, the child process performs only a small set of actions before it ceases execution of its program in favour of the program to be started, and it requires very few, if any, of its parent's data structures.

Chess

Chess is a two-player board game played on a chessboard, a checkered gameboard with 64 squares arranged in an eight-by-eight grid. Chess is played by millions of people worldwide, both amateurs and professionals.

Each player begins the game with 16 pieces: one king, one queen, two rooks, two knights, two bishops, and eight pawns. Each of the six piece types moves differently. The most powerful piece is the queen and the least powerful piece is the pawn. The objective is to 'checkmate' the opponent's king by placing it under an inescapable threat of capture. To this end, a player's pieces are used to attack and capture the opponent's pieces, while supporting their own. In addition to checkmate, the game can be won by voluntary resignation by the opponent, which typically occurs when too much material is lost, or if checkmate appears unavoidable. A game may also result in a draw in several ways.

Chess is believed to have originated in India, some time before the 7th century; the Indian game of chaturanga is also the likely ancestor of xiangqi and shogi. The pieces took on their current powers in Spain in the late 15th century; the rules were finally standardized in the 19th century.

Chess annotation symbols

When annotating chess games, commentators frequently use widely recognized annotation symbols. Question marks and exclamation points that denote a move as bad or good are ubiquitous in chess literature. Some publications intended for an international audience, such as the Chess Informant have a wide range of additional symbols that transcend language barriers.

The common symbols for evaluating the merits of a move are "??", "?", "?!", "!?", "!", and "!!". In these cases, the corresponding symbol is juxtaposed in the text immediately after the move (e.g. Re7? or Kh1!?, see algebraic chess notation).

Use of these annotation symbols is subjective, as different annotators use the same symbols differently. Moreover, an annotator's use of symbols is often influenced by the player's strength: a positional misjudgment that an annotator might give a "??" if played by a strong grandmaster might pass unremarked if played by a beginner.

Annotators' use of punctuation also may possibly be influenced by the result of the game (regardless of the actual quality of the move); one possible example came in the 11th game of the 1972 World Championship, when Spassky played an unexpected move, 14.Nb1, retreating the knight to its initial square. Spassky won the game, and several annotators gave the move two exclamation points. Edmar Mednis asserted that if Spassky had lost the game, the move would likely have been given two question marks instead.

Chess (OS X)

Chess is a 3D chess game for OS X, developed by Apple Inc. It supports chess variants such as crazyhouse and suicide chess. It originates in OpenStep and Mac OS X 10.2 and is based on open source software. Apple redistributes the source code under its own Apple Sample Code License.

Development

The game's front end is a Cocoa application whose drawing code is based on GNOME Chess. It communicates with the Sjeng chess engine which runs in a separate process. In OPENSTEP and OS X up to version 10.2 (Jaguar), Chess used bitmap graphics with a fixed, pseudo-3D perspective and used an early version of GNU Chess as the back-end engine.

Features

Chess can be also played using voice commands which uses OS X's built-in speech recognition capabilities. Games can be logged using the log feature, which can include information such as names, dates, places, types of game and moves made. In OS X Mountain Lion, Chess supports Game Center and in OS X Mavericks there is a voice-over which says "check" after playing the respective move.