---
title: "XY-Chain: Sudoku Technique #25 | Sudoku Flow"
description: "XY-Chain: In an XY-chain, the links force at least one of its two ends to hold their shared candidate, so any cell that sees both ends loses it."
url: https://sudokuflow.com/lessons/xyChain/
language: en
---

[Sudoku technique lessons](https://sudokuflow.com/lessons/) / XY-Chain

Lesson 25

# XY-Chain

## The rule

In an XY-chain, the links force at least one of its two ends to hold their shared candidate, so any cell that sees both ends loses it.

## Step by step

1. These 4 cells each hold just two candidates, and both end cells hold 3. Suppose the first end is not 3: then it is 5. Each link hands the next cell its other candidate (7, 2), so the last end is 3. Either way, one of the two ends is 3.
2. At least one end must be 3, so we can remove the candidate 3 from any other cell that sees both ends.

[Read the full lesson, with more examples →](https://sudoku.rubigogames.com/techniques/xy-chain.html)

In our app, when this technique is the next step, the hint names it and shows you why, step by step. No ads, free to download.

[App Store iPhone, iPad, Mac](https://apps.apple.com/app/apple-store/id6502922368?pt=125379530&ct=sudokuflow_cta&mt=8) [Google Play Android](https://play.google.com/store/apps/details?id=com.rubigogames.sudoku&referrer=utm_source%3Dsudokuflow%26utm_medium%3Dcta%26utm_campaign%3Dlesson)

## Try it on more boards

Each board is a real puzzle from our app, at a moment where XY-Chain applies. Find the step yourself, or tap Hint and the app's own hint walks you through it.

XY-Chain practice board:

```text
8* 3  7  | 9  1  4* | 5* 6* 2*
9  1* 4  | .  .  .  | 8  3* 7
.  .  2* | 8* 3  7* | 9* .  .
---------+----------+---------
3  7* 8  | .  9  .  | .  2  .
.  2  .  | 4  7* 3* | 6  8* .
.  .  6* | .  .  .  | 3* 7  .
---------+----------+---------
7* .  .  | 3* 4  .  | 2  .  6*
.  .  3  | 7  2  .  | .  9  8
2* .  1  | .  .  .  | 7* .  3
```
Digits marked * were filled in by a player; the others were printed with the puzzle.

![Sudoku app icon](https://sudokuflow.com/assets/app-icon.png)

## Want more boards like this?

We also make a Sudoku app for iPhone, iPad, Mac and Android. There are no ads in it at all, it works offline, and when you ask for a hint it shows you the technique instead of just filling in a number.

[App Store iPhone, iPad, Mac](https://apps.apple.com/app/apple-store/id6502922368?pt=125379530&ct=sudokuflow_web&mt=8) [Google Play Android](https://play.google.com/store/apps/details?id=com.rubigogames.sudoku&referrer=utm_source%3Dsudokuflow%26utm_medium%3Dweb%26utm_campaign%3Dsite)

Sudoku Flow is made by Rubigo Games, the developer of the Sudoku app recommended on this site.