Another Look at Nested Recursion

Functions specified by nested recursions are difficult to define and reason about. We present several ameliorative techniques that use deduction in a classical higher-order logic. First, we discuss how an apparent circular dependency between the proof of nested termination conditions and the definition of the specified function can be avoided. Second, we propose a method that allows the specified function to be defined in the absence of a termination relation. Finally, we show how our techniques extend to nested program schemes, where a termination relation cannot be found until schematic parameters have been filled in. In each of these techniques, suitable induction theorems are automatically derived.