Remote Pairs in Sudoku
Remote Pairs turn a string of look-alike cells into a chain of forced opposites. It is one of the friendliest chain techniques to learn.
A chain of twins
Sometimes several cells across the board all carry the exact same two candidates, say A and B. If those cells link up, each seeing the next through a shared unit, they form a chain. Along the chain the value flips. If the first is A, its neighbour must be B, the next A again, and so on.
Opposite ends
Because the values alternate, two cells an odd number of steps apart always end up opposite. One of them is A and the other is B, though you may not know which is which. That is enough. Between the two of them, both A and B are already committed.
The elimination
Any cell that can see both of those opposite ends cannot be A and cannot be B, since one of the ends has claimed each. You erase both candidates from it. Remote Pairs are a gentle first step into chain logic, and they build the habit of following links across the grid.
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