Extreme Used in extreme puzzles.
Grouped Chain (AIC)
Chains through groups
A group is a digit's places where a box and a row (or a column) cross, two or three of them, taken as one: it is true when one of them holds the digit, false when none does.
Groups link as single places do. When a digit's places in a unit split into two groups, or a group and a cell, one of the two holds it: a strong link. A group and a place of the same digit that sees all its cells cannot both hold it: a weak link.
A grouped AIC is an AIC, as in the chapter before, with groups among its nodes. One of its two ends is true, so a candidate that cannot stand with either goes: with the same digit at both ends, it goes from every cell that sees all the cells of both.
What to look for
Find a box where a digit's places line up: as a group, they link to the digit's other places along that line, as one place would.
Example
- The cells the technique relies on
- Cells where it removes candidates, struck out in red
- Strong link (solid line) and weak link (dashed)
Practise it
In the app, Learn › Grouped Chain (AIC) sets exercises on real positions, then a full puzzle that needs this technique and nothing harder.