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A Definitional TwoLevel Approach to Reasoning with HigherOrder Abstract Syntax
 Journal of Automated Reasoning
, 2010
"... Abstract. Combining higherorder abstract syntax and (co)induction in a logical framework is well known to be problematic. Previous work [ACM02] described the implementation of a tool called Hybrid, within Isabelle HOL, syntax, and reasoned about using tactical theorem proving and principles of (co ..."
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Cited by 24 (4 self)
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Abstract. Combining higherorder abstract syntax and (co)induction in a logical framework is well known to be problematic. Previous work [ACM02] described the implementation of a tool called Hybrid, within Isabelle HOL, syntax, and reasoned about using tactical theorem proving and principles of (co)induction. Moreover, it is definitional, which guarantees consistency within a classical type theory. The idea is to have a de Bruijn representation of syntax, while offering tools for reasoning about them at the higher level. In this paper we describe how to use it in a multilevel reasoning fashion, similar in spirit to other metalogics such as Linc and Twelf. By explicitly referencing provability in a middle layer called a specification logic, we solve the problem of reasoning by (co)induction in the presence of nonstratifiable hypothetical judgments, which allow very elegant and succinct specifications of object logic inference rules. We first demonstrate the method on a simple example, formally proving type soundness (subject reduction) for a fragment of a pure functional language, using a minimal intuitionistic logic as the specification logic. We then prove an analogous result for a continuationmachine presentation of the operational semantics of the same language, encoded this time in an ordered linear logic that serves as the specification layer. This example demonstrates the ease with which we can incorporate new specification logics, and also illustrates a significantly
Combining de Bruijn indices and higherorder abstract syntax in Coq
 Proceedings of TYPES 2006, volume 4502 of Lecture Notes in Computer Science
, 2006
"... Abstract. The use of higherorder abstract syntax is an important approach for the representation of binding constructs in encodings of languages and logics in a logical framework. Formal metareasoning about such object languages is a particular challenge. We present a mechanism for such reasoning, ..."
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Abstract. The use of higherorder abstract syntax is an important approach for the representation of binding constructs in encodings of languages and logics in a logical framework. Formal metareasoning about such object languages is a particular challenge. We present a mechanism for such reasoning, formalized in Coq, inspired by the Hybrid tool in Isabelle. At the base level, we define a de Bruijn representation of terms with basic operations and a reasoning framework. At a higher level, we can represent languages and reason about them using higherorder syntax. We take advantage of Coq’s constructive logic by formulating many definitions as Coq programs. We illustrate the method on two examples: the untyped lambda calculus and quantified propositional logic. For each language, we can define recursion and induction principles that work directly on the higherorder syntax. 1
On the proof theory of modal mucalculus
 Studia Logica
, 2008
"... We study the prooftheoretic relationship between two deductive systems for the modal mucalculus. First we recall an infinitary system which contains an omega rule allowing to derive the truth of a greatest fixed point from the truth of each of its (infinitely many) approximations. Then we recall a ..."
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Cited by 9 (2 self)
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We study the prooftheoretic relationship between two deductive systems for the modal mucalculus. First we recall an infinitary system which contains an omega rule allowing to derive the truth of a greatest fixed point from the truth of each of its (infinitely many) approximations. Then we recall a second infinitary calculus which is based on nonwellfounded trees. In this system proofs are finitely branching but may contain infinite branches as long as some greatest fixed point is unfolded infinitely often along every branch. The main contribution of our paper is a translation from proofs in the first system to proofs in the second system. Completeness of the second system then follows from completeness of the first, and a new proof of the finite model property also follows as corollary. 1
A proof pearl with the fan theorem and bar induction—Walking through infinite trees with mixed induction and coinduction
 In APLAS ’11
, 2011
"... Abstract. We study temporal properties over infinite binary redblue trees in the setting of constructive type theory. We consider several familiar pathbased properties, typical to lineartime and branchingtime temporal logics like LTL and CTL ∗ , and the corresponding treebased properties, in th ..."
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Abstract. We study temporal properties over infinite binary redblue trees in the setting of constructive type theory. We consider several familiar pathbased properties, typical to lineartime and branchingtime temporal logics like LTL and CTL ∗ , and the corresponding treebased properties, in the spirit of the modal μcalculus. We conduct a systematic study of the relationships of the pathbased and treebased versions of “eventually always blueness ” and mixed inductivecoinductive “almost always blueness ” and arrive at a diagram relating these properties to each other in terms of implications that hold either unconditionally or under specific assumptions (Weak Continuity for Numbers, the Fan Theorem, Lesser Principle of Omniscience, Bar Induction). We have fully formalized our development with the Coq proof assistant. 1
Formalization of CTL∗ in calculus of inductive constructions
, 2006
"... A modular formalization of the branching time temporal logic CTL∗ is presented. Our formalization subsumes prior formalizations of propositional linear temporal logic (PTL) and computation tree logic (CTL). Moreover, the modularity allows to instantiate our formalization for different formal securi ..."
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Cited by 3 (1 self)
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A modular formalization of the branching time temporal logic CTL∗ is presented. Our formalization subsumes prior formalizations of propositional linear temporal logic (PTL) and computation tree logic (CTL). Moreover, the modularity allows to instantiate our formalization for different formal security models. Validity of axioms and soundness of inference rules in axiomatizations of PTL, UB, CTL, and CTL∗ are discussed as well.
Modular Formalization of Reactive Modules in COQ ⋆
"... Abstract. We present modular formalizations of the model specification language Reactive Modules and the temporal logic CTL ∗ in the proof assistant Coq. In our formalizations, both shallow and deep embeddings of each language are given. The modularity of our formalizations allows proofs and theorem ..."
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Abstract. We present modular formalizations of the model specification language Reactive Modules and the temporal logic CTL ∗ in the proof assistant Coq. In our formalizations, both shallow and deep embeddings of each language are given. The modularity of our formalizations allows proofs and theorems to be reused across different embeddings. We illustrate the advantages of our modular formalizations by proving the mutual exclusion property of the Bakery algorithm in different embeddings. 1