Program development through proof transformation

We present a methodology for deriving veri ed programs that combines theorem proving and proof transformation steps. It extends the paradigm employed in systems like NuPrl where a program is developed and veri ed through the proof of the speci cation in a constructive type theory. We illustrate our methodology through an extended example | a derivation of Warshall's algorithm for graph reachability. We also outline how our framework supports the de nition, implementation, and use of abstract data types.