Latin Square

A Latin square is an n by n grid filled with n different symbols so that each symbol appears exactly once in every row and exactly once in every column. The name comes from Leonhard Euler's habit of using Latin letters as the symbols in his own papers on the subject, though a Latin square can be built from any set of n distinct symbols. The Korean mathematician Choi Seok-jeong published examples of order-nine Latin squares in 1700, more than sixty years before Euler began the general theory that made the name stick. A completed Sudoku grid is itself a Latin square of order nine, with the added rule that each of the nine three-by-three boxes must also contain every digit exactly once, and Latin squares are used more broadly in statistics, experimental design and error-correcting codes.