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This is a partially filled sudoku from the Sudoku Expert app.

enter image description here

I thought I learnt all tricks and techniques. But clearly there is something I don't know about.

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  • $\begingroup$ I got it from Sudoku Expert app. $\endgroup$ – Kashish Maheshwari Jan 6 at 12:19
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On the center rows, there are four squares which are either a 1 or a 5.

Now, what would happen if you put a

5 in row 8, column 2? That means row 5, column 8 is a 5 too, and row 6, column 9, a 1. Then there is no option for row 8, column 9. Therefore, the 5 in row 8 must be in column 9.

Schematic:

enter image description here

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  • $\begingroup$ You explanation seems incomplete. In row 8, column 2, you can put 1, 5 or 7 (1, 5 and 7 is also possible in row 7). 5 is not possible as explained. 1 would also not work work exactly the same reason. Thus, only 7 works there. Which give 1 in column 7 and finally 5 in column 9. $\endgroup$ – Phil1970 Jan 4 at 23:05
  • $\begingroup$ Wow. Why didn't I think of this before $\endgroup$ – Kashish Maheshwari Jan 6 at 12:29

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