Turbot Fish
A Turbot Fish is an open single-digit AIC with two strong-link nodes joined by a weak inference. If the first endpoint is false, the chain forces the far endpoint true. Therefore at least one endpoint is true—possibly both—and the digit can be removed from a candidate that sees both endpoints.
What is a Turbot Fish?
Write the construction as (A=B)-(C=D): A=B and C=D are exactly-one node pairs, while B-C means B and C cannot both be true. It follows that A or D is true. It does not follow that A and D always have opposite truth values.
How to spot it
For one digit, find two conjugate pairs and a valid weak inference between one candidate from each pair. Sharing a geometric point is not enough unless the candidate propositions are distinct and incompatible. The other ends are the elimination endpoints; a target must see both.
The logic
If A is false, B is true; because B and C cannot both be true, C is false; therefore D is true. Thus A or D is true. A target that sees both endpoints would make both false if it contained the digit, contradicting the chain, so the target candidate can be removed.