Recursive Function Definition for Types with Binders

This work describes the proof and uses of a theorem allowing definition of recursive functions over the type of λ-calculus terms, where terms with bound variables are identified up to α-equivalence. The theorem embodies what is effectively a principle of primitive recursion, and the analogues of this theorem for other types with binders are clear. The theorem's side-conditions require that the putative definition be well-behaved with respect to fresh name generation and name permutation. A number of examples over the type of X-calculus terms illustrate the use of the new principle.