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Let us solve the sudoku we have entered from a newspaper:

We look for a ‘single’, that is a square in which only one digit can be placed.

Such a square is I1 in row 1 where digit 7 must be.

(In row 1 digit 7 cannot be inside box J or box K, since both of these boxes already have digit 7.

Still looking at row 1, digit 7 cannot be in G1, since column G already has a 7.

Therefore the 7 in row 1 must be in square I1.)

To enter 7 in that square I1 we click it (see red arrow in the picture).

When you do that, a small window with the numbers 1 to 9 pops up at the side of square I1 (see below).

To enter 7 in the square you just click 7 in the popup window.

When you do that, 7 is placed in square I1 and the popup window disappears as shown below:

You can proceed entering digits in this way. In fact you can solve this sudoku just by locating squares in which only one digit can be placed (‘singles’).

If you do that you will arrive at this final solution:

Look here for more advanced solving techniques.

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