Monkeymore Sudoku

Unique Rectangle Type

Level 3 · Yellow Belt

Prerequisite: Unique RectanglesLearn next → Naked PairLearn next → Avoidable RectangleLearn next → Hidden Unique RectangleLearn next → Unique Rectangle Type 2Learn next → Unique Rectangle Type 3Learn next → Unique Rectangle Type 4Learn next → Unique Rectangle Type 5

Overview

Unique Rectangle Type 1 prevents a deadly pattern where four cells with identical candidate pairs would create multiple solutions. When three corners have only the pair and one has extras, the pair can be eliminated from the fourth.

How It Works

  1. Find four cells forming a rectangle across exactly two boxes.
  2. Three cells contain only candidates {X,Y}.
  3. The fourth cell contains {X,Y} plus additional candidates.
  4. Eliminate X and Y from the fourth cell to prevent the deadly pattern.

Example

Find four cells forming a rectangle across exactly 2 boxes, all containing candidates 7 and 8.

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Tips & Patterns

  • The rectangle must span exactly two rows, two columns, and two boxes.
  • This technique assumes the puzzle has a unique solution.
  • If X and Y remained in all four cells, they could be swapped infinitely.