Untyped algorithmic equality for Martin-Löf's logical framework with surjective pairs

Journal article, 2007

Martin-Löf's Logical Framework is extended by strong Sigma-types and presented via judgmental equality with rules for extensionality and surjective pairing. Soundness of the framework rules is proven via a generic PER model on untyped terms. An algorithmic version of the framework is given through an untyped beta eta-equality test and a bidirectional type checking algorithm. Completeness is proven by instantiating the PER model with eta-equality on beta-normal forms, which is shown equivalent to the algorithmic equality.