 Methods can also be employed to prevent essentially equivalent Sudokus from being redundantly tested.As a specific example, a search for a 17-clue Sudoku could start with a known 18-clue Sudoku, and then altering it by removing "three clues", and replacing them with only "two clues", in different positions (see last two images).This may discover new Sudokus, but there would be no immediate guarantee that they are essentially different from already known Sudokus.