Formal methods in transformational derivation of programs

Transformational derivation is the formal derivation of programs using the paradigm of program transformation. We discuss how formal methods of reasoning are used in this methodology. It is argued that formal methods, including induction, are essential for achieving common transformational objectives. Our discussion is in the context of the Focus system, an automated assistant to support program derivation using this paradigm. We illustrate how Focus provides support for rule management, rewriting, inductive reasoning and other formal activities, leaving the programmer free to explore high level design aspects.