 One of the main challenges for the proof-centered approach is that of distinguishing between rules that are genuinely meaning-determining and those that are not. Some rules for connectives, if added to a system, would lead to triviality. Prior (1960) offered the following rules for a connective “\(\tonk\)”. Its introduction rule says that from \(A\) one can infer \(A \tonk B\), and its elimination rule says that from \(A \tonk B\) one can infer \(B\). With the introduction of these rules, the system becomes trivial so long as at least one thing is provable, since from any assumption \(A\) one can derive any conclusion \(B\). Some constraints have to posed on inference rules, and much of subsequent literature has been concerned with these constraints (Belnap 1962, Dummett 1991, Prawitz 1974).