Tetris is a free tile-matching puzzle video game. The Tetris game is a popular use of tetrominoes, the four-element special case of polyominoes. Polyominoes have been used in popular puzzles since at least 1907, and the name was given by the mathematician Solomon W. Golomb in 1953. However, even the enumeration of pentominoes is dated to antiquity. The game (or one of its many variants) is available for nearly every video game console and computer operating system, as well as on devices such as graphing calculators, mobile phones, portable media players, PDAs, Network music players and even as an Easter egg on non-media products like oscilloscopes. It has even inspired Tetris serving dishes and been played on the sides of various buildings. "Tetriminos" are game pieces shaped like tetrominoes, geometric shapes composed of four square blocks each. A random sequence of Tetriminos fall down the playing field (a rectangular vertical shaft, called the "well" or "matrix"). The objective of the game is to manipulate these Tetriminos, by moving each one sideways (if the player feels the need) and rotating it by 90 degree units, with the aim of creating a horizontal line of ten units without gaps. When such a line is created, it disappears, and any block above the deleted line will fall. When a certain number of lines are cleared, the game enters a new level. As the game progresses, each level causes the Tetriminos to fall faster, and the game ends when the stack of Tetriminos reaches the top of the playing field and no new Tetriminos are able to enter. Some games also end after a finite number of levels or lines. All of the Tetriminos are capable of single and double clears. I, J, and L are able to clear triples. Only the I Tetrimino has the capacity to clear four lines simultaneously, and this is referred to as a "tetris". (This may vary depending on the rotation and compensation rules of each specific Tetris implementation. For instance, in the Super Rotation System used in most recent implementations, certain situations allow T, S, and Z to 'snap' into tight spots and clear triples.) The scoring formula for the majority of Tetris products is built on the idea that more difficult line clears should be awarded more points. For example, a single line clear in Tetris Zone is worth 100 points, clearing four lines at once (known as a Tetris) is worth 800, while a back-to-back Tetris is worth 1,200 each. Nearly all Tetris games allow the player to press a button to increase the speed of the current piece's descent, rather than waiting for it to fall. The player can also stop the pieces increased speed before the piece reaches the floor by letting go of the button, this is a "soft drop"; otherwise, it is a "hard drop" (some games only allow soft drop or hard drop; others have separate buttons). Many games award a number of points based on the height that the piece fell before locking.
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