Christian Urban, James Cheney, Stefan Berghofer. Mechanizing the Metatheory of LF. Extended tech report accompanying LICS 2008 paper.

LF is a dependent type theory in which many other formal systems can be conveniently embedded. However, correct use of LF relies on nontrivial metatheoretic developments such as proofs of correctness of decision procedures for LF's judgments. Although detailed informal proofs of these properties have been published, they have not been formally verified in a theorem prover. We have formalized these properties within Isabelle/HOL using the Nominal Datatype Package, closely following a recent article by Harper and Pfenning. In the process, we identified and resolved a gap in one of the proofs and a small number of minor lacunae in others. Besides its intrinsic interest, our formalization provides a foundation for studying the adequacy of LF encodings, the correctness of Twelf-style metatheoretic reasoning, and the metatheory of extensions to LF.

This paper is a substantial exercise in applying the approach of Harper and Licata in Mechanizing Language Definitions reported before, and is an advance towards a worthy objective in the campaign to mechanise metatheory that Paul espouses...

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