Graph theory for alternating hydrocarbons with attached ports

An anonymous referee showed us the existence of a linkable Δ-matroid with 7 ports that is not a Kekulé cell. The argument is presented. We classify the linkable cells with ≤5 ports and show that they all are Kekulé cells. We also classify the linkable cells with 6 ports. There are 214 classes; 210 classes contain Kekulé cells; only 4 classes are undecided.