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

# Almost Locked Set

An **Almost Locked Set** is a group of **N** cells in a single house with candidates for **N+1** digits. In other words, it is one cell short from being a locked set.

The simplest **ALS** is a single cell with 2 candidates. In a standard Sudoku an ALS can have a maximum size of 8 cells with 9 candidate digits.

It is not easy to spot a large ALS, but there are often a lot of these sets present in the grid. Bivalue cells are always easy to spot with pencilmarks.

## Usage

There are several solving techniques that make use of Almost Locked Sets. Any move that would eliminate all candidates for a particular digit from the ALS automatically forces the remaining digits to be locked in the group of cells. This the equivalent of a strong link, which can be used in chains and loops.

The ALS-XZ technique uses only 2 Almost Locked Sets to perform eliminations. It is the most basic ALS technique.

## See also

This page was last modified 16:19, 19 October 2008.