More about Free Web Sudoku 

Sudoku means "single digits. It is a trademark of  Nikoli Co. Ltd. Sudoku derives from the Japanese phrase "Suji wa dokushin ni kagiru," meaning "the numbers must be single," or "the numbers must occur only once."  The numerals in Sudoku puzzles are for convenience; arithmetic relationships between numerals are irrelevant.  Any set of distinct symbols will do; shapes, or colours may be used without altering the rules. In fact, ESPN published Sudoku puzzles substituting the positions on a baseball field for the numbers 1 through 9; and Viz magazine published a Doctor Who version of the game, using images of the television series' first nine leading actors in place of the numerals. Dell Magazines, the originator, has been using numerals for Number Place in its magazines since first published it in 1979.

The History of Sudoku before it hit the Web - Number puzzles first appeared in newspapers in the late 19th century, when French puzzle setters began experimenting with removing numbers from magic squares. Le Sicle, a Paris-based daily, published a partially completed 99 magic square with 33 sub-squares in 1892. It was not a Sudoku because it contained double-digit numbers and required arithmetic rather than logic to solve, but it shared key characteristics: each row, column and sub-square added up to the same number.

WebSudoku Hard - Within three years Le Sicle's rival, La France , refined the puzzle so that it was almost a modern web Sudoku. It simplified the 99 magic square puzzle so that each row and column contained only the numbers 19, but did not mark the sub-squares. Although they are unmarked, each 33 sub-square does indeed comprise the numbers 19. However, the puzzle cannot be considered the first Sudoku, under modern rules, it has two solutions. The puzzle setter ensured a unique solution by requiring 19 to appear in both diagonals.These weekly puzzles were a feature of newspaper titles including L'Echo de Paris for about a decade but disappeared about the time of the First World War.