145
Techniques · Medium
Hidden Pair
When two digits can only go in the same two cells of a unit, those cells are reserved for them. Any other candidates in those two cells can be removed.
How to spot it
In a unit, find two digits that each have exactly two possible cells, and the cells are the same. The pair is often hidden among other notes; strip the extras and it becomes a Naked Pair.
Example
3
15
4589
489
158
2
6
7
2
145
7
345
6
135
13
8
9
9
6
8
237
237
1237
5
4
13
8
125
9
257
27
4
167
3
156
6
25
35
1
237
9
4
257
8
4
7
135
6
238
2358
9
25
15
5
3
4
79
1
6
8
79
2
7
9
26
238
5
238
36
1
4
1
8
26
23479
23479
237
367
579
356
In column 5, 4 and 9 can only go in r1c5 and r9c5, so all other candidates can be removed from those cells (Hidden Pair).
the pattern cells that lose a candidate (crossed out)