Uniqueness

The uniqueness family

PREVENT A SECOND SOLUTION BY RECOGNIZING DEADLY CONFIGURATION.

Uniqueness techniques use an additional assumption common to valid classic Sudoku puzzles: the puzzle is intended to have one unique solution. When a candidate pattern could create two valid completions, that pattern cannot be allowed to remain. They require a specific candidate configuration and a clear uniqueness proof.

There are two set of uniqueness family: Unique Rectangles, and BUGs:

A Unique Rectangle is a "deadly" pattern of four cells occupying exactly two rows, two columns and two boxes, each cell contains the same two candidates.

A BUG stands for a Bivalue Universal Grave, it is an invalid state where every unsolved cell has only two candidates and every candidates. appears exactly twice in every row, column and box.

Each family has various techniques to break those invalid deadly patterns to ensure a valid Sudoku puzzle have one unique solution.

The question: Would leaving these candidates unresolved create a second solution?