   which simply says that if \(f (r\) any truth-value) then \(f(rq)\) for arbitrary \(q\), and that it obviously correct. It can be (tediously) checked that the result is valid for all sixteen extensional binary truth-functions substitutable for ‘\(f\) ’. Dragging the whole of Protothetic out of these simple beginnings is obviously much harder, and depends on coming up with suitable definitions for the connectives.