Suppose you have the following in the boxes 1 and 2, where '*' means, there may be any candidates (also 3).

- Code: Select all
`16 * * | * 36 14 |`

25 * 1256| 45 * 23 |

* 123 1256| * * * |

Then r3c2 is 3.

To clarify the technique, this is the beginners version:

- Code: Select all
`15 * * | 12 45 * |`

* * 24 | 12 45 * |

45 123 * | * * * |

I leave it up to you to classify all the variations of this fabulous technique