 Observe that a heterogenous definition such as (4) is not a mere abbreviation. For, if it were, the expression \(x\) in it would not be a genuine variable, and the definition would provide no guidance on the role of \(G\) in contexts other than \(Gx\). Moreover, if such definitions were abbreviations, they would be subject to the requirement that the definiendum must be shorter than the definiens, but no such requirement exists. On the other hand, genuine requirements on definitions would make little sense. The following stipulation is not a legitimate definition: