Guess

A digit placed into a cell without a logical reason.

A controversial way to solve a Sudoku, usually employed when the player cannot advance using the solving techniques he or she has mastered. When the guess leads immediately to the solution, the player has found a backdoor. Alternatively, when the guess leads to a contradiction, the player must backtrack to the state before the digit was placed and he or she can eliminate the candidate for that digit. This method is also known as Trial & Error.

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