The last Sudoku entry discussed the *uniqueness* rule. As an
extreme example, the last 20 clues in this board may be filled in using
only this rule. No need to use elimination at all!

Note that the boxes are numbered from 1 at the upper left to 9 at the bottom right.

The solution:

Cell 4,2 is the unique possible location for a 5 in col 4

Cell 6,8 is the unique possible location for a 5 in col 6

Cell 5,2 is the unique possible location for a 1 in box 2

Cell 9,3 is the unique possible location for a 1 in box 3

Cell 1,7 is the unique possible location for a 9 in box 7

Cell 5,8 is the unique possible location for a 8 in box 8

Cell 3,2 is the unique possible location for a 9 in row 2

Cell 2,3 is the unique possible location for a 2 in row 3

Cell 8,7 is the unique possible location for a 4 in row 7

Cell 7,8 is the unique possible location for a 3 in row 8

Cell 1,1 is the unique possible location for a 4 in col 1

Cell 9,9 is the unique possible location for a 5 in col 9

Cell 3,1 is the unique possible location for a 7 in box 1

Cell 7,9 is the unique possible location for a 2 in box 9

Cell 3,4 is the unique possible location for a 8 in col 3

Cell 7,6 is the unique possible location for a 8 in col 7

Cell 8,4 is the unique possible location for a 5 in row 4

Cell 2,6 is the unique possible location for a 4 in row 6

Cell 2,5 is the unique possible location for a 6 in col 2

Cell 8,5 is the unique possible location for a 3 in col 8

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