Expert technique · Technique Academy

Empty Rectangle

An Empty Rectangle is a box where one digit's candidates lie only along a single row and a single column of that box, leaving an empty rectangle in the rest. Combined with a line elsewhere where the digit has just two places, it forces an elimination.

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

The reasoning

Why does the Empty Rectangle work?

Either the digit is on the box's row, which forces the other cell of the two-place line, or it is on the box's column, which covers the target directly. Either way, the cell where the free cell's row meets that column loses the digit.

A worked example

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

Empty Rectangle worked exampleA sudoku board with pencil marks. The Empty Rectangle uses R2C1, R3C3, R8C1, R8C9 and digit 2 (box 1). The move strikes candidate 2 in R3C9.143278679279527862379541237592741237682373267127841277956798549637237192671272375123783674671852436796792639178542642756391278
The move strikes candidate 2 in R3C9. Digit 2, box 1.
  • Cells that form the pattern
  • Cells that lose a candidate
  • Struck digit: ruled out

Make it stick

How can you practise the Empty 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.

Easier2-String KiteHarderXYZ-Wing