Monkeymore Sudoku

Empty Rectangle

Level 5 · Orange Belt

Prerequisite: Single-Digit PatternsLearn next → Locked Candidates

Overview

Empty Rectangle uses the absence of a candidate in a rectangular area within a box. When four cells form an empty rectangle for a candidate, combined with a strong link, eliminations become possible.

How It Works

  1. Find a box where a candidate forms an "L" shape (all instances in one row and one column of the box).
  2. The remaining 4 cells form an empty rectangle for that candidate.
  3. Find a strong link outside the box that shares a line with the non-empty row/column.
  4. Eliminate from the intersection of the other strong link cell's line and the box's non-empty column/row.

Example

Check digit 9 in box 7. All candidates form an 'L' or 'T' shape.

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Tips & Patterns

  • Empty Rectangles are easier to find when you look for the "L" pattern first.
  • The technique exploits that the candidate must be in one of the L's arms.
  • Practice identifying Empty Rectangle Intersections (ERIs).