Bialgebraic Reasoning on Higher-order Program Equivalence

Logical relations constitute a key method for reasoning about contextual equivalence of programs in higher-order languages.They are usually developed on a per-case basis, with a new theory required for each variation of the language or of the desired notion of equivalence.In the present paper we introduce a general construction of (step-indexed) logical relations at the level of Higher-Order Mathematical Operational Semantics, a highly parametric categorical framework for modeling the operational semantics of higherorder languages.Our main result states that for languages whose weak operational model forms a lax bialgebra, the logical relation is automatically sound for contextual equivalence.Our abstract theory is shown to instantiate to combinatory logics and -calculi with recursive types, and to different flavours of contextual equivalence.