 As is clear, an application of the rule requires that a consistency condition be satisfied. What makes meeting the condition complicated is the fact that rules can interact in complex ways. In particular, it is possible that an application of some rule might cause the consistency condition to fail for some, not necessarily distinct, rule. For instance, if \(\theta\) is \(\neg\tau\) then an application of the rule is in a sense self-defeating, in that an application of the rule itself causes the consistency condition to fail. 