--- title: "Sue de Coq: Sudoku Technique #35 | Sudoku Flow" description: "Sue de Coq: When cells at a box-line crossing collectively have two more distinct candidates than cells, a bivalue helper outside the box in the line and…" url: https://sudokuflow.com/lessons/sueDeCoq/ language: en --- [Sudoku technique lessons](https://sudokuflow.com/lessons/) / Sue de Coq Lesson 35 # Sue de Coq ## The rule When cells at a box-line crossing collectively have two more distinct candidates than cells, a bivalue helper outside the box in the line and another outside the line in the box can draw disjoint pairs from that pool. Every pool digit must then be placed exactly once among the crossing cells and helpers. The line helper's digits can be removed from the line outside the crossing cells and that helper; the box helper's digits can be removed from the box outside the crossing cells and that helper. Any pool digits in neither helper are confined to the crossing cells and can be removed from both the line and the box outside those cells. ## Step by step 1. These 2 cells sit where the outlined box crosses a column. Together they hold 4 different candidates, two more than the number of cells, so every digit that lands in them must come from that small pool. 2. Two more helper cells take their candidates from the same pool, and each of them has only two candidates left. One helper is in the same column and its two candidates are 2, 6. The other is in the same box and its two candidates are 3, 8. The two pairs have no candidate in common. So there are now 4 cells and 4 digits: the crossing cells and the two helpers each take a different digit from the pool, and every pool digit is used exactly once. 3. However the digits fall, 2, 6 can only be in the crossing cells or in the column helper, and 3, 8 can only be in the crossing cells or in the box helper. So we can remove 2, 6 from all the remaining cells of the column, and 3, 8 from all the remaining cells of the box. [Read the full lesson, with more examples →](https://sudoku.rubigogames.com/techniques/sue-de-coq.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 Sue de Coq applies. Find the step yourself, or tap Hint and the app's own hint walks you through it. Sue de Coq practice board: ```text 9* 8 3 | 2* 5 6 | 7* 1* 4* 2 5 7* | 8* 4 1* | 9 3 6* 6* 1* 4 | 7 9* 3* | 8* 2* 5 ---------+----------+--------- . . . | 5* . . | 3* 4 1* 5* 4* 1 | 3 6* 8* | . 9* . 3* . . | . . 4* | 5 6 8 ---------+----------+--------- . 6 . | . 8 . | 4* . 3* . 3 . | 4 . . | . . . 4 . . | 6* 3* 5 | 1 . 9 ``` 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.