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Golden Chains

Eduyng Castano writes to me about a Sudoku solving technique he has discovered. Here is his paper describing what he calls Golden Chains (pdf).

The technique is a generalization of XY-Wing that identifies exclusion pairs connected by chains of arbitrary length. It solves many (but not all) of the same puzzles that can be solved by other advanced techniques such as conjugate pairs, nishio and coloring. Unlike those techniques, Golden Chains is a pattern-matching technique (like XY-Wing), and does not feel so much like a fishing expedition, or guessing.

I have successfully used it to solve a number of my ‘super tough’ puzzles. Golden Chains is particularly effective when a puzzle has been reduced to a lot of squares containing only 2 possibilities.

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