Extreme technique · Technique Academy

X-Chain

An X-Chain follows one digit along a chain of cells linked alternately by strong links, units where the digit has only two places, and weak links, where it merely cannot be in both. It is Simple Coloring's wilder cousin.

Professor Cryptic, the owl who teaches in the app
Professor Cryptic is thinking

The reasoning

Why does the X-Chain work?

If the chain begins and ends on strong links, one of its two end cells must hold the digit. Any cell that sees both ends cannot hold it, and you strike it there.

A worked example

What does the X-Chain look like on a real board?

X-Chain worked exampleA sudoku board with pencil marks. The X-Chain uses R4C1, R4C7, R3C7, R3C5, R1C4, R9C4 and digit 3 (6 cells). The move strikes candidate 3 in R9C1.9726838235123641324632687824712695451259234623781327569138489421375613653648792133543591372867978169453223623937584179
The move strikes candidate 3 in R9C1. Digit 3, 6 cells.
  • Cells that form the pattern
  • Cells that lose a candidate
  • Struck digit: ruled out

Make it stick

How can you practise the X-Chain?

The Technique Academy in Cryptic gives every technique its own lesson and 5 practice boards that need exactly this move.

Get it onGoogle PlayPlay Cryptic on the web

Further reading: HoDoKu's page on this family of techniques.

EasierXY-Chain