Extreme technique · Technique Academy

Unique Rectangle

A Unique Rectangle is four cells in two rows, two columns and two boxes that could all hold the same pair of digits, which would let you swap them and get a second solution. Since a proper puzzle has one solution, the rectangle cannot be left that way.

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

The reasoning

Why does the Unique Rectangle work?

In the simplest form, three corners hold only the pair and the fourth holds extra candidates, so the fourth cannot be either of the pair. Strike the pair from it.

A worked example

What does the Unique Rectangle look like on a real board?

Unique Rectangle worked exampleA sudoku board with pencil marks. The Unique Rectangle uses R3C7, R3C8, R6C7, R6C8 and digits 1, 3 (R3C7 to R6C8). The move strikes candidates 1 in R3C7, 3 in R3C7.2673839513694781679387843652543827961391378395417826816523794724696981313598714526365273948143168682579
The move strikes candidates 1 in R3C7, 3 in R3C7. Digits 1, 3, R3C7 to R6C8.
  • Cells that form the pattern
  • Cells that lose a candidate
  • Struck digit: ruled out

Make it stick

How can you practise the Unique Rectangle?

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.

EasierBUG+1HarderSimple Coloring