Given the complexity of the metatheoretic reasoning involved with current programming languages and their type systems, techniques for mechanical formalization and checking of the metatheory have received much recent attention. In previous work, we advocated a combination of locally nameless representation and cofinite quantification as a lightweight style for carrying out such formalizations in the Coq proof assistant. As part of the presentation of that methodology, we described a number of operations associated with variable binding and listed a number of properties, called “infrastructure lemmas, ” about those operations that needed to be shown. The proofs of these infrastructure lemmas are generally straightforward, given a specification of the binding structure of the language. In this work, we present LNgen, a prototype tool for automatically generating these definitions, lemmas, and proofs from Ott-like language specifications. Furthermore, the tool also generates a recursion scheme for defining functions over syntax, which was not available in our previous work. We also show the soundness and completeness of our tool’s output. For untyped lambda terms, we prove the adequacy of our representation with respect to a fully concrete representation, and we argue that the representation is complete—that we generate the right set of lemmas—with respect to Gordon and Melham’s “Five Axioms of Alpha-Conversion. ” Finally, we claim that our recursion scheme is simpler to work with than either Gordon and Melham’s recursion scheme or the recursion scheme of Nominal Logic. 1.

Abstract. Psi-calculi are extensions of the pi-calculus, accommodating arbitrary nominal datatypes to represent not only data but also communication channels, assertions and conditions, giving it an expressive power beyond the applied pi-calculus and the concurrent constraint picalculus. We have formalised psi-calculi in the interactive theorem prover Isabelle using its nominal datatype package. One distinctive feature is that the framework needs to treat binding sequences, as opposed to single binders, in an efficient way. While different methods for formalising single binder calculi have been proposed over the last decades, representations for such binding sequences are not very well explored. The main effort in the formalisation is to keep the machine checked proofs as close to their pen-and-paper counterparts as possible. We discuss two approaches to reasoning about binding sequences along with their strengths and weaknesses. We also cover custom induction rules to remove the bulk of manual alpha-conversions. 1

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We describe in this paper formalisations for the properties of weakening, type-substitutivity, subject-reduction and terminationof the usual big-step evaluation relation. Our language is the lambda-calculus whose simplicity allows us to give theoremprover code for the formal proofs. The formalisations are done in the theorem prover Isabelle/HOL using the nominal datatypepackage. The point of these formalisations is to be as close as possible to the "pencil-and-paper" proofs for these properties, but of course be completely rigorous. We describe where the nominal datatype package is of great help with such formalisationsand where one has to invest additional effort in order to obtain formal proofs.

Abstract. We present a Nominal Isabelle formalization of an expressive core fragment of XQuery, a W3C standard functional language for querying XML documents. Our formalization focuses on results presented in the literature concerning XQuery’s operational semantics, typechecking, and optimizations. Our core language, called mini-XQuery, omits many complications of XQuery such as ancestor and sibling axes, recursive types and functions, node identity, and unordered processing modes, but does handle distinctive features of XQuery including monadic comprehensions, downward XPath steps and regular expression types. To our knowledge no language with similar features has been mechanically formalized previously. Our formalization is a first step towards a complete formalization of full XQuery and may also be useful as a benchmark for comparing other mechanized metatheory tools. 1

Abstract: This paper is about completely formal representation of languages with binding. We have previously written about a representation following an approach going back to Frege, based on first-order syntax using distinct syntactic classes for locally bound variables vs. \ global or free variables. The present paper differs from our previous work by being more abstract. Whereas we previously gave a particular concrete function for canonically choosing the names of binders, here we characterize abstractly the properties required of such a choice function to guarantee canonical representation, and focus on the metatheory of the representation, proving that it is in substitution preserving isomorphism with the nominal Isabelle representation of pure lambda terms. This metatheory is formalized in Isabelle/HOL. The final section outlines a formalization in Matita of a challenging language with multiple binding and simultaneous substitution. The Isabelle and Matita proof files are available online. Click here to download Manuscript: paper.tex Click here to view linked References 1 2