Mirrored from **Sudopedia**, the Free Sudoku Reference Guide

# Unique Rectangle

A **Unique Rectangle** is a Deadly Pattern formed by 4 cells that share 2 rows, 2 columns and 2 boxes. In Sudoku Variations with additional constraints, each of these constraints must either contain 2 cells or none at all. All 4 cells only have candidates for the same 2 digits.

The name is not well chosen. The pattern causes the puzzle to have at least 2 solutions, so a better name would be **non-unique rectangle**.

Here is an example:

Rows 1 and 2, columns 1 and 4 and boxes 1 and 2 each contain 2 cells from this pattern. All cells have candidates 1 and 2. There are 2 ways to complete this pattern.

A more concrete example:

This puzzle has two solutions.

## A mistake to be avoided

The following pattern is sometimes mistaken for a unique rectangle. However, this pattern occupies 4 boxes.

This is not a unique rectangle!

## See also

This page was last modified 07:59, 22 January 2009.