Medium

Hidden pair

What it is

Two digits that can only go in the same two cells of a unit – all other candidates in those cells can be removed.

Count where each digit can go in a row, column or box. If two digits both fit only in the same two cells, those cells are reserved for them.

In row 1, 1 and 8 only appear in r1c3 and r1c6. Those cells must hold 1 and 8, so 3 and 4 are removed from r1c3, and 6 and 7 from r1c6.

Used from level: Medium