To fill in more possibilities you could look through each cell and count all the numbers in the same block, column, and row, but I personally find this to be too much work with too little gain and cannot be bothered to show it. Most sudoku puzzles are made so that there is only one final solution after sifting through all the options and filling in all the blocks. For the same reason the naked twin also eliminates 2 from square Cc and a 4 must go there.
Whenever you allocate a square this may, in turn, unlock other squares so it is worth restarting the same procedure over for the whole grid. Only a 5,6 and 9 can appear in those three locations. Look at this 4x4 grid. Andrew Stuart writes:. Remember, true Sudoku puzzles have one and only one correct solution. The logic being that since those 2 cells were the only ones with those 2 numbers, neither of them could have been any other number so they were erased.
Doing this by hand is laborious and prone to error, and often detracts from the fun of solving these puzzles. You can share your tips and experiences on our strategy message forum.
Each row, column, and nonet can contain each number typically 1 to 9 exactly once. Every row and column has three sub-groups in the three regions it crosses.
This same logic applies when a puzzle that has two columns where candidate C is restricted to exactly the same two rows. If these candidates are found in other cells in the group they can be excluded.
Solving with Colors: The extra candidates in the cell "hide" the single solution. The two 'twin' rules are particular examples of the general Sudoku logic. Thomas Kuhler Hello, My hobby is geocaching. Well I have some good news. Another Sudoku tip is to look for "naked triples".
OR the numbers could be switched around and still create a working solution.
Sudoku Dragon has been used with possibilities enabled and exclusions switched on so that the grid directly shows the squares where the exclusion rule comes into play.