this paper, we do this by adding the #-quantifier: its role will be to declare variables to be new and of local scope. The syntax of the formula # x.B is like that for the universal and existential quantifiers. Following Church's Simple Theory of Types [Church 1940], formulas are given the type o, and for all types # not containing o, # is a constant of type (# o) o. The expression # #x.B is ACM Transactions on Computational Logic, Vol. V, No. N, October 2003. 4 usually abbreviated as simply # x.B or as if the type information is either simple to infer or not important

We present a meta-logic that contains a new quantifier (for encoding "generic judgment") and inference rules for reasoning within fixed points of a given specification. We then specify the operational semantics and bisimulation relations for the finite π-calculus within this meta-logic. Since we

Bedwyr is a generalization of logic programming that allows model checking directly on syntactic expressions possibly containing bindings. This system, written in OCaml, is a direct implementation of two recent advances in the theory of proof search. The first is centered on the fact that both finite success and finite failure can be captured in the sequent calculus by incorporating inference rules for definitions that allow fixed points to be explored. As a result, proof search in such a sequent calculus can capture simple model checking problems as well as may and must behavior in operational semantics. The second is that higherorder abstract syntax is directly supported using term-level λ-binders and the quantifier known as ∇. These features allow reasoning directly on expressions containing bound variables. 2

This paper describes a general method of compiler implementation using higher order abstract syntax and logic programming. A working compiler written in Prolog is used to demonstrate this method.

Many semantical aspects of programming languages are specified through calculi for constructing proofs: consider, for example, the specification of structured operational semantics, labeled transition systems, and typing systems. Recent proof theory research has identified two features that allow direct, logic-based reasoning about such descriptions: the treatment of atomic judgments as fixed points (recursive definitions) and an encoding of binding constructs via generic judgments. However, the logics encompassing these two features have thus far treated them orthogonally. In particular, they have not contained the ability to form definitions of object-logic properties that themselves depend on an intrinsic treatment of binding. We propose a new and simple integration of these features within an intuitionistic logic enhanced with induction over natural numbers and we show that the resulting logic is consistent. The pivotal part of the integration allows recursive definitions to define generic judgments in general and not just the simpler atomic judgments that are traditionally allowed. The usefulness of this logic is illustrated by showing how it can provide elegant treatments of object-logic contexts that appear in proofs involving typing calculi and arbitrarily cascading substitutions in reducibility arguments.

We describe the design of a rule-based language for expressing changes to Haskell programs in a systematic and reliable way. The update language essentially offers update commands for all constructs of the object language (a subset of Haskell). The update language can be translated into a core calculus consisting of a small set of basic updates and update combinators. The key construct of the core calculus is a scope update mechanism that allows (and enforces) update specifications for the definition of a symbol together with all of its uses. The type of an update program is given by the possible type changes it can cause for an object programs. We have developed a typechange inference system to automatically infer type changes for updates. Updates for which a type change can be successfully inferred and that satisfy an additional structural condition can be shown to preserve type correctness of object programs. In this paper we define the Haskell Update Language HULA and give a translation into the core update calculus. We illustrate HULA and its translation into the core calculus by several examples.

The operational semantics of programming and specification languages is often presented via inference rules and these can generally be mapped into logic programming-like clauses. Such logical encodings of operational semantics can be surprisingly declarative if one uses logics that directly account for term-level bindings and for resources, such as are found in linear logic. Traditional theorem proving techniques, such as unification and backtracking search, can then be applied to animate operational semantic specifications. Of course, one wishes to go a step further than animation: using logic to encode computation should facilitate formal reasoning directly with semantic specifications. We outline an approach to reasoning about logic specifications that involves viewing logic specifications as theories in an object-logic and then using a meta-logic to reason about properties of those object-logic theories. We motivate the principal design goals of a particular meta-logic that has been built for that purpose.

Abstract. We give a logic programming language based on Fiore, Plotkin and Turi’s binding algebras. In this language, we can use not only first-order terms but also terms involving variable binding. The aim of this language is similar to Nadathur and Miller’s λProlog, which can also deal with binding structure by introducing λ-terms in higher-order logic. But the notion of binding used here is finer in a sense than the usual λ-binding. We explicitly manage names used for binding and treat α-conversion with respect to them. Also an important difference is the form of application related to β-conversion, i.e. we only allow the form (M x), where x is a (object) variable, instead of usual application (M N). This notion of binding comes from the semantics of binding by the category of presheaves. We firstly give a type theory which reflects this categorical semantics. Then we proceed along the line of first-order logic programming language, namely, we give a logic of this language, an operational semantics by SLD-resolution and unification algorithm for binding terms. 1

Some recent theoretical work in proof search has illustrated that it is possible to combine the following two computational principles into one computational logic. 1. A symmetric treatment of finite success and finite failure. This allows capturing both aspects of may and must behavior in operational semantics and mixing model checking and logic programming. 2. Direct support for λ-tree syntax, as in λProlog, via term-level λ-binders, higher-order pattern unification, and the ∇-quantifier. All these features have a clean proof theory. The combination of these features allow, for example, specifying rather declarative approaches to model checking syntactic expressions containing bindings. The Bedwyr system is intended as an implementation of these computational logic principles. Why the name Bedwyr? In the legend of King Arthur and the round table, several knights shared in the search for the holy grail. The name of one of them, Parsifal, is used for an INRIA team associated with the “Slimmer ” effort. Bedwyr was another one of those knights. Wikipedia (using the spelling “Bedivere”) mentions that Bedwyr appears in Monty Python and the Holy Grail where he is “portrayed as a master of the extremely odd logic in the ancient times, whom occasionally blunders. ” Bedwyr is a re-implementation and rethinking ∗ Support has been obtained for this work from the following sources: from INRIA through

High-level formalisms for reasoning about names and binding such as de Bruijn indices, various flavors of higher-order abstract syntax, the Theory of Contexts, and nominal abstract syntax address only one relatively restrictive form of scoping: namely, unary lexical scoping, in which the scope of a (single) bound name is a subtree of the abstract syntax tree (possibly with other subtrees removed due to shadowing). Many languages exhibit binding or renaming structure that does not fit this mold. Examples include binding transitions in the #-calculus; unique identifiers in contexts, memory heaps, and XML documents; declaration scoping in modules and namespaces; anonymous identifiers in automata, type schemes, and Horn clauses; and pattern matching and mutual recursion constructs in functional languages. In these cases, it appears necessary to either rearrange the abstract syntax so that lexical scoping can be used, or revert to first-order techniques. The purpose