# sudoku

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explanations:-
this is step:- 4

Only one place for a 3 in box 6
. Therefore only one cell left for the 2 at c7r4.
That 2 in row 4 makes a 5 in column 2. Now the 2 and 5 are chosen it can only be a 6 in c4r4.
There is now only one place for a 3 in box 5 and finally an 8 in the last cell c9r4.

That 8 in box 6 makes c9r6 a 7 with a 6 in the last cell.

Column c8 has only the three cells left in box 9 with 2, 6 and 9 possible. Therefore 2, 6 and 9 cannot be elsewhere in box 9 so time to clean up the possibles ...

.

c1
c2
c3

c4
c5
c6

c7
c8
c9

7 8
 49
1
 49
 3
3

 6
6
 5
5
2
r1
box

1
2
&
3
 259
 box 1
1
 259

 2579
 2579
6
 37
3
 box 3
8
4
r2
 56
3
 456
8
 45
 27
2
1
 37
7
9
r3
4
 25
5
7
 256
6
 235678
3
9
 28
2
1
 68
8
r4
box

4
5
&
6
 82
 box 4
9
3
 267
 12678
 178
5
 box 6
4
 678
6
r5
 825
6 1   4
 23578
 178
9
 23
3
 78
7
r6
3
 257
8
 2679
 12679
4
 27
 269
 1567
r7
box

7
8
&
9
 2569
 box 7
4
 2569
3
 126789
 178

 278
 269
 15678
r8
1
 27
 269

 2679
 26789
5   4
 269
3
r9
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