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On behalf of co-authors Christian Urban and Stefan Berghofer, we are happy to announce the availability of the following technical report. This an extended version of a paper to appear in LICS 2008. Comments are very welcome. --James Cheney http://arxiv.org/abs/0804.1667 Mechanizing the Metatheory of LF Christian Urban, James Cheney and Stefan Berghofer Abstract: 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.