Tetromino

A tetromino is a shape made up of four squares directly connected to each other by their edges.[1][2]

The five free tetrominoes

If one considers a tetromino that has been moved (translated), turned (rotated) or flipped (reflected) to be the same shape, there are five distinct tetrominoes. These are known as free tetrominoes.

Tetrominoes are well known for being the game pieces used in the video game Tetris, which was created by Alexey Pajitnov.[3] Tetris uses one-sided tetrominoes, which can be translated and rotated but not reflected. This makes for a total of seven tetrominoes.

References
  1. Golomb, Solomon W. (1994). Polyominoes (2nd ed.). Princeton, New Jersey: Princeton University Press. ISBN 0-691-02444-8.
  2. Redelmeier, D. Hugh (1981). "Counting polyominoes: yet another attack". Discrete Mathematics. 36 (2): 191–203. doi:10.1016/0012-365X(81)90237-5.
  3. "About Tetris", Tetris.com. Retrieved 2014-04-19.
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