Remote Pairs
A chain of four or more bivalue cells all holding the same {X, Y} candidates. The endpoints hold OPPOSITE digits — any cell that sees both endpoints loses both X and Y.
Advanced sudoku technique
What it is
A Remote Pair is a chain of an EVEN number of bivalue cells (4, 6, 8, ...), all sharing the same two candidates {X, Y}, where consecutive cells in the chain share a unit (row, column, or box). Because each connection forces alternating X/Y assignments along the chain, the two endpoints must hold OPPOSITE values — one endpoint is X and the other is Y (we don't yet know which is which). Therefore any cell that sees BOTH endpoints can't be X (the X endpoint blocks it via shared unit) AND can't be Y (the Y endpoint blocks it). Eliminate both digits.
When to use it
On master and evil-tier puzzles. Hunt for chains of 4+ bivalue cells with the same candidate pair.
Worked example
Bivalue chain on {3, 8}: R2C2 → R2C7 (row 2 link) → R8C7 (column 7 link) → R8C2 (row 8 link). That's a 4-cell chain. The endpoints R2C2 and R8C2 sit in column 2; one holds 3, the other holds 8. Any cell in column 2 between them that sees both drops both 3 and 8 from its candidates.
Try it
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