Me too. I understand the first rule (LN -m->PriComm), but I thought the "only" meant if a supplier is a large nursery, then any raspberry plant they sell must be disease-free. I'm confused!

Really like this approach as well! Mine is a lot less sophisticated, but based on our lessons so far I differentiate the two by:

Negating: It is not the case that [statement] --> falsifying

Contrapositive: It can also be said that [statement] --> still true