Revisiting an automatic program inverter for Lisp

Abstract

We reformulate the Korf-Eppstein method for automatic inversion of first-order functional programs using a structural operational semantics and compare it with the program inversion method described by Gries. We analyze the method and suggest possible extensions. The method is noteworthy in that it was used to construct the first automatic program inverter described in the literature. The key features of the Korf-Eppstein method are the simultaneous inversion of an injective system of functions, an equation-oriented transformation, and the use of postcondition inference heuristics.