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Arctic Sudoku
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ExpertKiller

Chains with cage links

What it is

A cage that must hold a digit in one of two cells works as a strong link in a chain.

How to spot it

When a cage's digit can only be in two of its cells, treat them as a strong link and continue the chain through ordinary rows, columns and boxes.

Example

123456123431212131516
  • Basis
  • Removed / placed
The cage of 3 is 1+2, so 1 is in r1c1 or r1c2. If it isn't in r1c1, it's in r1c2; then it's not in r5c2, so row 5's other place, r5c3, is 1. Either r1c1 or r5c3 is 1, so 1 is removed from r4c1, which sees both.

Used from level: Expert (Killer Sudoku)