arXiv subjects

Colin Riba

Publications and source records attributed to Colin Riba.

9 recordsLinked to original sources

arXiv2026

A Complete Finitary Refinement Type System for Scott-Open Properties

We are interested in proving input-output properties of functions that handle infinite data such as streams or non-wellfounded trees. We provide a finitary refinement type system which is (sound and) complete for Scott-open properties defined in a fixpoint-like logic. Working on top of Abramsky's Domain Theory in Logical Form, we build from the well-known fact that the Scott domains interpreting recursive types are spectral spaces. The usual symmetry between Scott-open and compact-saturated sets is reflected in logical polarities: positive formulae allow for least fixpoints and define Scott-open sets, while negative formulae allow for greatest fixpoints and define compact-saturated sets. A realizability implication with the expected (contra)variance on polarities allows for non-trivial input-output properties to be formulated as positive formulae on function types.

cs.LO↗

arXiv2025

Infinitary Refinement Types for Temporal Properties in Scott Domains

We discuss an infinitary refinement type system for input-output temporal specifications of functions that handle infinite objects like streams or infinite trees. Our system is based on a reformulation of Bonsangue and Kok's infinitary extension of Abramsky's Domain Theory in Logical Form to saturated properties. We show that in an interesting range of cases, our system is complete without the need of an infinitary rule introduced by Bonsangue and Kok to reflect the well-filteredness of Scott domains.

cs.LO↗

arXiv2023

Liveness Properties in Geometric Logic for Domain-Theoretic Streams

We devise a version of Linear Temporal Logic (LTL) on a denotational domain of streams. We investigate this logic in terms of domain theory, (point-free) topology and geometric logic. This yields the first steps toward an extension of the "Domain Theory in Logical Form" paradigm to temporal liveness properties. We show that the negation-free formulae of LTL induce sober subspaces of streams, but that this is in general not the case in presence of negation. We propose a direct, inductive, translation of negation-free LTL to geometric logic. This translation reflects the approximations used to compute the usual fixpoint representations of LTL modalities. As a motivating example, we handle a natural input-output specification for the usual filter function on streams.

cs.LO↗

arXiv2023

Finitely accessible arboreal adjunctions and Hintikka formulae

Arboreal categories provide an axiomatic framework in which abstract notions of bisimilarity and back-and-forth games can be defined. They act on extensional categories, typically consisting of relational structures, via arboreal adjunctions. In many cases, equivalence of structures in fragments of infinitary first-order logic can be captured by transferring the bisimilarity relation along the adjunction. In most applications, the categories involved are locally finitely presentable and the adjunctions are finitely accessible. Our main result identifies the expressive power of this class of adjunctions. We show that the ranks of back-and-forth games in the arboreal category are definable by formulae \`a la Hintikka, and thus the relation between extensional objects induced by bisimilarity is always coarser than equivalence in infinitary first-order logic. Our approach leverages Gabriel-Ulmer duality for locally finitely presentable categories, and Hodges' word-constructions.

cs.LO↗

arXiv2019

A Functional (Monadic) Second-Order Theory of Infinite Trees

This paper presents a complete axiomatization of Monadic Second-Order Logic (MSO) over infinite trees. MSO on infinite trees is a rich system, and its decidability ("Rabin's Tree Theorem") is one of the most powerful known results concerning the decidability of logics. By a complete axiomatization we mean a complete deduction system with a polynomial-time recognizable set of axioms. By naive enumeration of formal derivations, this formally gives a proof of Rabin's Tree Theorem. The deduction system consists of the usual rules for second-order logic seen as two-sorted first-order logic, together with the natural adaptation In addition, it contains an axiom scheme expressing the (positional) determinacy of certain parity games. The main difficulty resides in the limited expressive power of the language of MSO. We actually devise an extension of MSO, called Functional (Monadic) Second-Order Logic (FSO), which allows us to uniformly manipulate (hereditarily) finite sets and corresponding labeled trees, and whose language allows for higher abstraction than that of MSO.

cs.LO↗

arXiv2018

A Curry-Howard Approach to Church's Synthesis

Church's synthesis problem asks whether there exists a finite-state stream transducer satisfying a given input-output specification. For specifications written in Monadic Second-Order Logic (MSO) over infinite words, Church's synthesis can theoretically be solved algorithmically using automata and games. We revisit Church's synthesis via the Curry-Howard correspondence by introducing SMSO, an intuitionistic variant of MSO over infinite words, which is shown to be sound and complete w.r.t. synthesis thanks to an automata-based realizability model.

cs.LO↗

arXiv2011

On the confluence of lambda-calculus with conditional rewriting

The confluence of untyped λ-calculus with unconditional rewriting is now well un- derstood. In this paper, we investigate the confluence of λ-calculus with conditional rewriting and provide general results in two directions. First, when conditional rules are algebraic. This extends results of Müller and Dougherty for unconditional rewriting. Two cases are considered, whether β-reduction is allowed or not in the evaluation of conditions. Moreover, Dougherty's result is improved from the assumption of strongly normalizing β-reduction to weakly normalizing β-reduction. We also provide examples showing that outside these conditions, modularity of confluence is difficult to achieve. Second, we go beyond the algebraic framework and get new confluence results using a restricted notion of orthogonality that takes advantage of the conditional part of rewrite rules.

cs.LO↗

arXiv2006

Combining typing and size constraints for checking the termination of higher-order conditional rewrite systems

In a previous work, the first author extended to higher-order rewriting and dependent types the use of size annotations in types, a termination proof technique called type or size based termination and initially developed for ML-like programs. Here, we go one step further by considering conditional rewriting and explicit quantifications and constraints on size annotations. This allows to describe more precisely how the size of the output of a function depends on the size of its inputs. Hence, we can check the termination of more functions. We first give a general type-checking algorithm based on constraint solving. Then, we give a termination criterion with constraints in Presburger arithmetic. To our knowledge, this is the first termination criterion for higher-order conditional rewriting taking into account the conditions in termination.

cs.LO↗

arXiv2006

On the confluence of lambda-calculus with conditional rewriting

The confluence of untyped lambda-calculus with unconditional rewriting has already been studied in various directions. In this paper, we investigate the confluence of lambda-calculus with conditional rewriting and provide general results in two directions. First, when conditional rules are algebraic. This extends results of Muller and Dougherty for unconditional rewriting. Two cases are considered, whether beta-reduction is allowed or not in the evaluation of conditions. Moreover, Dougherty's result is improved from the assumption of strongly normalizing beta-reduction to weakly normalizing beta-reduction. We also provide examples showing that outside these conditions, modularity of confluence is difficult to achieve. Second, we go beyond the algebraic framework and get new confluence results using an extended notion of orthogonality that takes advantage of the conditional part of rewrite rules.

cs.LO↗