---
title: "ALS: Connect almost locked candidate groups"
description: "An ALS is a group of n cells in one area with n+1 distinct digits among their candidates. Two such groups can interact through a restricted common candidate."
lang: "en"
canonical: "https://unisu-sudoku.app/en/sudoku-techniques/als/"
---

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Master class

# ALS: Connect almost locked candidate groups

An ALS is a group of n cells in one area with n+1 distinct digits among their candidates. Two such groups can interact through a restricted common candidate.

![Unisu lesson on ALS, showing the explained grid](https://unisu-sudoku.app/_astro/en.DYI8bIku_1pvRuI.webp)

An ALS is a group of n cells in one area with n+1 distinct digits among their candidates. Two such groups can interact through a restricted common candidate.

Two cells see each other when they share a row, column or 3×3 box. An elimination needs the specific visibility relationships described in the reasoning.

## An example from the app

Group A: E7, F7. Group B: C8, F8.

Group A has 2 cells with 5, 8, 9. Group B has 2 cells with 4, 5, 8. Each group has exactly one more candidate digit than cells. They are two separate ALSs.

Every possible 8 in A shares a row, column or box with every possible 8 in B. So 8 cannot occur in both groups. At least one group must do without it.

Without 8, that group has exactly as many digits as cells and needs all of them, including 5. So 5 occurs in A or B. Cells sharing an area with every 5 position in both groups lose it.

These notes are therefore ruled out: D8: 5.

The image shows the candidates relevant to this step. A note being hidden does not mean it has been logically eliminated.

## Practice the next step

In this ALS-XZ example the groups do not overlap. The linking candidate cannot appear in both groups at once. Another common candidate can be removed from a cell seeing all its positions in both groups.

In the app, follow the reasoning in the matching lesson and try a task yourself. With a new puzzle, always start from its actual candidate state.

## Questions about ALS

### Does n+1 count notes or distinct digits?

Distinct candidate digits. Repeated occurrences of one digit count only once for this condition.

### Can an ALS use arbitrary cells across the grid?

No. Its n cells must share an area and contain exactly n+1 distinct candidate digits between them.

### What is a restricted common candidate?

Every position for that digit in one group sees every position in the other. The digit therefore cannot appear in both groups together.

### Can the two groups overlap?

They are disjoint in the ALS-XZ case explained here. The illustrated argument depends on those separate groups.

### Must the target see every cell of both groups?

It must see every position of the digit being eliminated in both groups. Seeing one arbitrary cell from each is insufficient.

## Keep practicing in Unisu

Download Unisu for iPhone or Android. Solve a puzzle or work through a guided lesson on the technique.

-   [Download on the App Store](https://apps.apple.com/us/app/id6775824061?l=en)
-   [Get it on Google Play](https://play.google.com/store/apps/details?id=app.unisu.sudoku&hl=en)

## Useful before this guide

### Naked Pair

[Read more: Naked Pair](https://unisu-sudoku.app/en/sudoku-techniques/naked-pair/)

### AIC

[Read more: AIC](https://unisu-sudoku.app/en/sudoku-techniques/aic/)

## Where to go next

Master class

Unisu · Oct 27, 2026

### [Forcing Chain: Examine two possibilities separately](https://unisu-sudoku.app/en/sudoku-techniques/forcing-chain/)

A Forcing Chain checks both candidates of a cell in separate branches. If both branches force the same elimination, you can apply it with certainty.

Unisu

### [Learn Sudoku: a path from rules to techniques – Unisu](https://unisu-sudoku.app/en/learn/)

Start with the rules, get comfortable with pencil marks and choose a technique for the situation you’re working on.

Download app

## Ready for a puzzle? Take a moment.

Download Unisu on your phone. Start a Sudoku or choose a lesson on the technique you want to understand.

-   [Download on the App Store](https://apps.apple.com/us/app/id6775824061?l=en)
-   [Get it on Google Play](https://play.google.com/store/apps/details?id=app.unisu.sudoku&hl=en)

![The daily challenge in Unisu](https://unisu-sudoku.app/_astro/en.C-sYR9hJ_1QwI9G.webp)

![A classic Sudoku game in Unisu](https://unisu-sudoku.app/_astro/en.C6DJ1kiE_2dRWDN.webp)