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Octavio Malherbe

Publications and source records attributed to Octavio Malherbe.

17 recordsLinked to original sources
arXiv2025

Basis-Sensitive Quantum Typing via Realisability

We present $\lambda_B$, a quantum-control $\lambda$-calculus that refines previous basis-sensitive systems by allowing abstractions to be expressed with respect to arbitrary -- possibly entangled -- bases. Each abstraction and let construct is annotated with a basis, and a new basis-dependent substitution governs the decomposition of value distributions. These extensions preserve the expressive power of earlier calculi while enabling finer reasoning about programs under basis changes. A realisability semantics connects the reduction system with the type system, yielding a direct characterisation of unitary operators and ensuring safety by construction. From this semantics we derive a validated family of typing rules, forming the foundation of a type-safe quantum programming language. We illustrate the expressive benefits of $\lambda_B$ through examples such as Deutsch's algorithm and quantum teleportation, where basis-aware typing captures classical determinism and deferred-measurement behaviour within a uniform framework.

cs.LO↗
arXiv2025

An Algebraic Extension of Intuitionistic Linear Logic: The $L_!^S$-Calculus and Its Categorical Model

We introduce the $L_!^S$-calculus, a linear lambda-calculus extended with scalar multiplication and term addition, that acts as a proof language for intuitionistic linear logic (ILL). These algebraic operations enable the direct expression of linearity at the syntactic level, a property not typically available in standard proof-term calculi. Building upon previous work, we develop the $L_!^S$-calculus as an extension of the $L^S$-calculus with the $!$ modality. We prove key meta-theoretical properties--subject reduction, confluence, strong normalisation, and an introduction property--as well as preserve the expressiveness of the original $L^S$-calculus, including the encoding of vectors and matrices, and the correspondence between proof-terms and linear functions. A denotational semantics is provided in the framework of linear categories with biproducts, ensuring a sound and adequate interpretation of the calculus. This work is part of a broader programme aiming to build a measurement-free quantum programming language grounded in linear logic.

cs.LO↗
arXiv2024

Beyond Monads and Biproducts: A Uniform Interpretation of Parallelism in Intuitionistic Logic

Traditional approaches to modelling parallelism and algebraic structure in lambda calculi often rely on monads$\unicode{x2013}$as in Moggi's framework$\unicode{x2013}$or on rich categorical structures such as biproducts$\unicode{x2013}$as used in certain models of linear logic. In this work, we propose a minimal alternative that captures both parallelism and weighted parallelism (linear combinations) within the setting of intuitionistic propositional logic, without resorting to monads or assuming the existence of biproducts. We introduce two lambda calculi: a parallel lambda calculus and an algebraic lambda calculus, both extending full propositional intuitionistic logic. Their semantics are given in two categories: ${\mathbf{Mag}_{\mathbf{Set}}}$, whose objects are magmas and arrows are functions in $\mathbf{Set}$; and ${\mathbf{AMag}^{\mathcal{S}}_{\mathbf{Set}}}$, whose objects are action magmas. The key technical challenge addressed is the interpretation of disjunction in the presence of parallel and algebraic operators. Since the usual coproduct structure is unavailable in our minimal setting, we propose a novel set-theoretic interpretation based on the union of the disjoint union and the Cartesian product. This allows for the construction of sound and adequate models for both calculi. Our results offer a unified and structurally lightweight framework for modelling parallelism and algebraic effects in intuitionistic logic, opening the way to alternatives beyond the traditional monadic or linear logic approaches.

cs.LO↗
arXiv2023

A General Probabilistic Framework in IMALL: A Concrete Categorical Perspective

We consider the linear lambda-calculus extended with the sup type constructor, which provides an additive conjunction along with a non-deterministic destructor. The sup type constructor has been introduced in the context of quantum computing. In this paper, we study this type constructor within a simple linear logic categorical model, employing the category of semimodules over a commutative semiring. We demonstrate that the non-deterministic destructor, either weighted or not, finds a suitable model in a weighted codiagonal map. Our approach offers a valid and insightful alternative to interpreting non-determinism and probability calculi, in instances where the conventional Moggi's Powerset Monad interpretation does not align with the category's structure, as is the case with the category of semimodules. The validity of this alternative relies on the presence of biproducts within the category.

cs.LO↗
arXiv2022

Quantum Control in the Unitary Sphere: Lambda-S1 and its Categorical Model

In a recent paper, a realizability technique has been used to give a semantics of a quantum lambda calculus. Such a technique gives rise to an infinite number of valid typing rules, without giving preference to any subset of those. In this paper, we introduce a valid subset of typing rules, defining an expressive enough quantum calculus. Then, we propose a categorical semantics for it. Such a semantics consists of an adjunction between the category of distributive-action spaces of value distributions (that is, linear combinations of values in the lambda calculus), and the category of sets of value distributions.

cs.LO↗
arXiv2022

The Sup Connective in IMALL: A Categorical Semantics

We explore a proof language for intuitionistic multiplicative additive linear logic, incorporating the sup connective that introduces additive pairs with a probabilistic elimination, and sum and scalar products within the proof-terms. We provide an abstract characterisation of the language, revealing that any symmetric monoidal closed category with biproducts and a monomorphism from the semiring of scalars to the semiring Hom(I,I) is suitable for the job. Leveraging the binary biproducts, we define a weighted codiagonal map which is at the core of the sup connective.

cs.LO↗
arXiv2020

A categorical construction for the computational definition of vector spaces

Lambda-S is an extension to first-order lambda calculus unifying two approaches of non-cloning in quantum lambda-calculi. One is to forbid duplication of variables, while the other is to consider all lambda-terms as algebraic linear functions. The type system of Lambda-S has a constructor S such that a type A is considered as the base of a vector space while S(A) is its span. Lambda-S can also be seen as a language for the computational manipulation of vector spaces: The vector spaces axioms are given as a rewrite system, describing the computational steps to be performed. In this paper we give an abstract categorical semantics of Lambda-S* (a fragment of Lambda-S), showing that S can be interpreted as the composition of two functors in an adjunction relation between a Cartesian category and an additive symmetric monoidal category. The right adjoint is a forgetful functor U, which is hidden in the language, and plays a central role in the computational reasoning.

cs.LO↗
arXiv2019

The category of implicative algebras and realizability

In this paper we continue with the algebraic study of Krivine's realizability, refining some of the authors' previous constructions by introducing two categories, with objects the abstract Krivine structures and the implicative algebras respectively. These categories are related by an adjunction whose existence clarifies many aspects of the theory previously established.

math.LO↗
arXiv2018

A concrete model for a typed linear algebraic lambda calculus

We give an adequate, concrete, categorical-based model for Lambda-S, which is a typed version of a linear-algebraic lambda calculus, extended with measurements. Lambda-S is an extension to first-order lambda calculus unifying two approaches of non-cloning in quantum lambda-calculi: to forbid duplication of variables, and to consider all lambda-terms as algebraic linear functions. The type system of Lambda-S have a superposition constructor S such that a type A is considered as the base of a vector space while SA is its span. Our model considers S as the composition of two functors in an adjunction relation between the category of sets and the category of vector spaces over C. The right adjoint is a forgetful functor U, which is hidden in the language, and plays a central role in the computational reasoning.

cs.LO↗
arXiv2016

Linear Hyperdoctrines and Comodules

In this exposition, we get examples of what is called a "linear hyperdoctrine", based on categories of comodules indexed by coalgebras. This structures can model first order linear logic.

math.LO↗
arXiv2015

Realizability in OCAs and AKSs

In the context of the $\mathcal{OCA}$ associated to an ${\mathcal{AKS}}$ we introduce a closure operator and two associated maps that replace the closure and the maps defined in \cite{kn:ocar}. We were motivated by the search of a full adjunction to the original implication map. We show that all the constructions from $\mathcal{OCA}$s to triposes developped in \cite{kn:ocar} can be also implemented in the new situation.

math.LO↗
arXiv2014

Ordered combinatory algebras and realizability

We consider different classes of combinatory structures related to Krivine realizability. We show, in the precise sense that they give rise to the same class of triposes, that they are equivalent for the purpose of modeling higher-order logic. We center our attentions in the role of a special kind of Ordered Combinatory Algebras-- that we call the "Krivine ordered combinatory algebras" ($\mathcal{KOCA}$s)-- that we propose as the foundational pillars for the categorical perspective of Krivine's classical realizability as presented by Streicher. Our procedure is the following: we show that each of the considered combinatory structures gives rise to an indexed preorder, and describe a way to transform the different structures into each other that preserves the associated indexed preorders up to equivalence. Since all structures give rise to the same indexed preorders, we only prove that they are triposes once: for the class of $\mathcal{KOCA}$s. We finish showing that in $\mathcal{KOCA}$s, one can define realizability in every higher-order language and in particular in higher-order arithmetic.

math.LO↗
arXiv2013

A Report on Realizability

Besides recalling the basic definitions of Realizability Lattices, Abstract Krivine Structures, Ordered Combinatory Algebras and Tripos and reviewing its relationships, we propose a new foundational framework for realizability. Motivated by Streicher's paper "Krivine's Classical Realizability from a Categorical Perspective" [9], we define the concept of Krivine's Ordered Combinatory Algebras (kOKA) as a common platform that is strong enough to do both: categorical and computational semantics. The OCAs produced by Streicher from AKSs in [9] are particular cases of kOKAs.

math.LO↗
arXiv2013

Presheaf models of quantum computation: an outline

This paper outlines the construction of categorical models of higher-order quantum computation. We construct a concrete denotational semantics of Selinger and Valiron's quantum lambda calculus, which was previously an open problem. We do this by considering presheaves over appropriate base categories arising from first-order quantum computation. The main technical ingredients are Day's convolution theory and Kelly and Freyd's notion of continuity of functors. We first give an abstract description of the properties required of the base categories for the model construction to work. We then exhibit a specific example of base categories satisfying these properties.

math.CT↗
arXiv2013

Categorical models of computation: partially traced categories and presheaf models of quantum computation

This dissertation has two main parts. The first part deals with questions relating to Haghverdi and Scott's notion of partially traced categories. The main result is a representation theorem for such categories: we prove that every partially traced category can be faithfully embedded in a totally traced category. Also conversely, every monoidal subcategory of a totally traced category is partially traced, so this characterizes the partially traced categories completely. The main technique we use is based on Freyd's paracategories, along with a partial version of Joyal, Street, and Verity's Int construction. Along the way, we discuss some new examples of partially traced categories, mostly arising in the context of quantum computation. The second part deals with the construction of categorical models of higher-order quantum computation. We construct a concrete semantic model of Selinger and Valiron's quantum lambda calculus, which has been an open problem until now. We do this by considering presheaf categories over appropriate base categories arising from first-order quantum computation. The main technical ingredients are Day's convolution theory and Kelly and Freyd's notion of continuity of functors. We first give an abstract description of the properties required of the base categories for the model construction to work; then exhibit a specific example of base categories satisfying these properties.

math.CT↗
arXiv2012

Partially traced categories

This paper deals with questions relating to Haghverdi and Scott's notion of partially traced categories. The main result is a representation theorem for such categories: we prove that every partially traced category can be faithfully embedded in a totally traced category. Also conversely, every symmetric monoidal subcategory of a totally traced category is partially traced, so this characterizes the partially traced categories completely. The main technique we use is based on Freyd's paracategories, along with a partial version of Joyal, Street, and Verity's Int-construction.

math.CT↗