[tadfisher]

Yeah, that example is bad. The query doesn't require recursion, but they affirm it does by demonstrating a recursively-defined version of it. This is called "affirming the consequent"; "P -> Q" doesn't mean "Q -> P". Ironic, given the use of propositional logic throughout.

[evnc]

doh, good point. will fix this, I acknowledge I sort of handwaved the example. thanks for the correction!