 Although Gold talks in developmental psycholinguistic terms about language learners learning grammars by trial and error, his extremely abstract proofs actually make no reference to the linguistic content of languages or grammars at all. The set of all finite grammars formulable in any given metalanguage is computably enumerable, so grammars can be systematically numbered. Inputs—grammatical expressions from the target language—can also be numerically encoded. We end up being concerned simply with the existence or non-existence of certain functions from natural number sequences to natural numbers.