 How strong a claim (RR) is depends on what counts as a rule. If an arbitrary function deserves that name, the rule-to-rule principle is stronger than  (C):  it is equivalent to local, distributive, language bound compositionality of meaning. But if we insist—quite plausibly—that a semantic rule must be computable (or perhaps easily computable) the rule-to-rule principle is stronger than that. And if we assume that rules must have some sort of psychological reality, (RR) says something completely different from  (C).  