Making Substitutions Explicit in SASyLf

Abstract

SASyLF is an interactive proof assistant whose goal is to teach: about type systems, language meta-theory, and writing proofs in general. This software tool stores user-specified languages and logics in the dependently-typed LF, and its internal proof structure closely resembles M2+ . This thesis describes a new usability feature of SASyLF, “where” clauses, which make explicit previously hidden substitutions that arise through constructs in the proof code, primarily case analyses. An overview of SASyLF and logical frameworks is given, with motivating examples. The requirements for “where” clauses are discussed, including a formal definition of correctness. The feature’s implementation in SASyLF is outlined, and future extensions are discussed.