Same-Digit Two-Strong-Link Chains
A same-digit two-strong-link chain, often shortened to two-strong-link chain, is the simplest kind of alternating inference chain (AIC). It contains four nodes involving the same candidate digit, connected by three links in the pattern strong-weak-strong. The name refers to the two strong links in this pattern.
If you draw the strong links on the board, they often form some recognizable shapes:
- Skyscraper: the two strong links are parallel.
- Two-String Kite: the two strong links are perpendicular.
- Turbot Fish: one of the two strong links is tucked inside a box.
Another same-digit two-strong-link chain, the Empty Rectangle, uses grouped nodes for one of its strong links.