Mirrored from Sudopedia, the Free Sudoku Reference Guide

# Sudopedia:Fish diagram

When a solving technique only deals with the candidates for a single digit, it is customary to use the letter X to replace this digit, both in chain notation and in the illustrating diagrams. This abstraction helps the reader understand that this is a single-digit technique and focus on the pattern rather than the pencilmarked candidates.

You are advised to use fish diagrams to illustrate these techniques. These diagrams are based on a text format used in fish-related topics in the Sudoku Players' forum.

Here is an example, illustrating a Finned Swordfish:

This is the same example in the text format used in the forums:

```.  /  . | .  /  . | .  /  .
*  X  * | .  X  . | .  X  .
.  F  . | .  /  . | .  /  .
--------+---------+--------
.  /  . | .  /  . | .  /  .
.  X  . | .  X  . | .  X  .
.  /  . | .  /  . | .  /  .
--------+---------+--------
.  /  . | .  /  . | .  /  .
.  X  . | .  X  . | .  X  .
.  /  . | .  /  . | .  /  .
```

If you do not have the tools to create graphical fish diagrams, use the text version instead. Sooner or later, a helpful Sudopedian will replace it with a graphical version.

## Symbols

There are only a few symbolic characters used in fish diagrams.

/ (forward slash)
Cells that do not contain a candidate for digit X. These cells belong to the defining set.
X
Cells that may contain a candidate for digit X. These cells belong to both the defining set and the secondary set.
*
Cells from which the candidates for digit X can be eliminated. These cells only belong to the secondary set.
F
Fin cells. These only belong to the defining set, but are limited to a single house.
. (dot)
Irrelevant cells. These are unmarked in the graphical version of the diagram.