Remote Pairs
A chain of identical two-candidate cells colours into two answers.
Learn the Remote Pairs Sudoku technique: a chain of identical two-candidate cells alternates between two answers, so a cell seeing both ends loses both digits.
How to use it
- Find a chain of identical pairs. Locate four or more cells that all carry the exact same two candidates, each linked to the next because they share a row, column, or box.
- Colour the chain. Tag the cells alternately with two colours along the chain. One colour will end up holding the first digit and the other the second — you do not yet know which way round.
- Eliminate from cells seeing both colours. Whatever the orientation, any outside cell that sees a cell of each colour sees both digits, so remove both of those candidates from it.