Sudoku solving techniques: focus on a cell

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The other way around is to focus on the position of a cell and logically eliminate which number should be there. Take a look at the below example which focuses on the cell in 6th row and 7th position:

6 9 8 3 7 4 5 2 1
9 4
5 4 2 9 7 3
2 5 8 9
9 2
2 3 1
7 3 2 4 5
2
1 2 6 9

When you start eliminating numbers based on which are already in that block, row (6) and column (7) you’ll discover that the only option for the cell is 4.