Paul Taylor

Jean-Yves Girard

Yves Lafont

Proofs and types

These lectures on logic, more specifically proof theory, are basically intended for postgraduate students and researchers in logic. The question at stake is the nature of mathematical knowledge and the difference between a question and an answer, i.e., the implicit and the explicit. The problem is delicate mathematically and philosophically as well: the relation between a question and its answer is a sort of equality where one side is ``more equal than the other'': one thus discovers essentialist blind spots. Starting with Godel's paradox (1931)--so to speak, the incompleteness of answers with respect to questions--the book proceeds with paradigms inherited from Gentzen's cut-elimination (1935). Various settings are studied: sequent calculus, natural deduction, lambda calculi, category-theoretic composition, up to geometry of interaction (GoI), all devoted to explicitation, which eventually amounts to inverting an operator in a von Neumann algebra. Mathematical language is usually described as referring to a preexisting reality. Logical operations can be given an alternative procedural meaning: typically, the operators involved in GoI are invertible, not because they are constructed according to the book, but because logical rules are those ensuring invertibility. Similarly, the durability of truth should not be taken for granted: one should distinguish between imperfect (perennial) and perfect modes. The procedural explanation of the infinite thus identifies it with the unfinished, i.e., the perennial. But is perenniality perennial? This questioning yields a possible logical explanation for algorithmic complexity. This highly original course on logic by one of the world's leading proof theorists challenges mathematicians, computer scientists, physicists, and philosophers to rethink their views and concepts on the nature of mathematical knowledge in an exceptionally profound way.

Lectures on Logic

The Blind Spot

L'expérience de la connaissance nous enseigne qu'il n'y a pas de Réalité Dernière, que tout train en cache un autre. Une évidence qu'il n'est pas facile d'accepter, d'où l'idée de ce train ultime, celui qui ne cacherait plus rien. La transparentisme postule l'existence, au-delà de la perception immédiate, d'un monde, d'un niveau de lecture, complètement intelligible, i.e, explicite et immédiat. D'où cette croyance en de prétendus "rayons X du savoir" qui nous dévoileraient l'envers de l'Univers.

Le Fantôme de la transparence

Michelle Labrèche-Larouche

André Ducharme

Quel sens donnez-vous à votre vie? Qu'est-ce qui vous rend heureux? Quels sont vos craintes et vos espoirs? Voici 20 entretiens avec des personnalités de divers horizons qui nous parlent de leur parcours, de leurs petits et grands bonheurs, du sens qu'elles donnent à leur vie, mais aussi du deuil et de la mort. Des propos d'une grande sensibilité, tantôt étonnants, tantôt émouvants, et qui appellent à la réflexion.

Le sens de la vie selon 20 personnalités

À propos de la vie

Philip Scott

Thomas Ehrhard

Paul Ruet

This book illustrates linear logic in the application of proof theory to computer science.

Linear Logic in Computer Science

This book constitutes the refereed proceedings of the 4th International Conference on Typed Lambda Calculi and Applications, TLCA'99, held in L'Aquila, Italy in April 1999. The 25 revised full papers presented were carefully reviewed and selected from a total of 50 submissions. Also included are two invited demonstrations. The volume reports research results on various aspects of typed lambda calculi. Among the topics addressed are noncommutative logics, type theory, algebraic data types, logical calculi, abstract data types, and subtyping.

Jean-Yves Girard

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