Expert technique · Technique Academy

Hidden Quad

A hidden quad is four digits that, within one unit, can only go in the same four cells. Those cells look crowded with other candidates, which turn out to be irrelevant.

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

The reasoning

Why does the Hidden Quad work?

The four digits must fill the four cells, so every other candidate in those cells can be struck out. Few players find one by eye, and fewer admit it.

A worked example

What does the Hidden Quad look like on a real board?

Hidden Quad worked exampleA sudoku board with pencil marks. The Hidden Quad uses R2C8, R2C9, R3C8, R3C9 and digits 2, 5, 7, 9 (box 3). The move strikes candidates 2 in R2C8, 5 in R2C8, 5 in R3C8, 9 in R3C8, 7 in R3C9, 9 in R3C9.568927691614681348348176941598316125271736842156168158978925686859473891394183927653958715936915624894896732591481484842931857681567492323
The move strikes candidates 2 in R2C8, 5 in R2C8, 5 in R3C8, 9 in R3C8, 7 in R3C9, 9 in R3C9. Digits 2, 5, 7, 9, box 3.
  • Cells that form the pattern
  • Cells that lose a candidate
  • Struck digit: ruled out

Make it stick

How can you practise the Hidden Quad?

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.

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