UA68/7/2/2 Picnic Program

Program: Le Cercle Francais presents son pique-nique annuel a Kittlestic

UA68/7/2/2 Club Bulletin, No. 1

Bulletin created by Le Cercle Francais in French

UA68/7/2/2 Club Bulletin, No. 2

Bulletin created by Le Cercle Francais in French

UA68/7/2/2 Club Bulletin, No. 5

Bulletin created by Le Cercle Francais in French

UA68/7/2/2 Club Bulletin, No. 3

Bulletin created by Le Cercle Francais in French

Existential witness extraction in classical realizability and via a negative translation

We show how to extract existential witnesses from classical proofs using Krivine's classical realizability---where classical proofs are interpreted as lambda-terms with the call/cc control operator. We first recall the basic framework of classical realizability (in classical second-order arithmetic) and show how to extend it with primitive numerals for faster computations. Then we show how to perform witness extraction in this framework, by discussing several techniques depending on the shape of the existential formula. In particular, we show that in the Sigma01-case, Krivine's witness extraction method reduces to Friedman's through a well-suited negative translation to intuitionistic second-order arithmetic. Finally we discuss the advantages of using call/cc rather than a negative translation, especially from the point of view of an implementation.Comment: 52 pages. Accepted in Logical Methods for Computer Science (LMCS), 201

The Architectural Illusion of Edoardo Tresoldi: The Reconstruction of the Basilica of Siponto

The Ministry of Tourism commissioned Edoardo Tresoldi in 2016 to restore the Basilica of Siponto (Puglia, Italy), of which only ruins remain. The project is obtained through metal wefts that intertwine in the air presumably reconstructing the original environments: it is an example of creative restoration. This essay aims to examine the genesis of this artwork that has rekindled the debate on the usefulness of this type of restoration, introduced for the first time by Cesare Brandi (1906-1988) and Renato Bonelli (1911-2004) who gave rise to a critical discussion on the role that restoration must play in reconstructing the original spaces of a lost monument. Creative restoration tends to include in the concept of “restoration” all those actions of reconstruction necessary to restore “truth” to the lost monument in order to guarantee its enjoyment, making the “evocative fantasy” take over. Faced with an architecture that has now lost its face, the added value of Tresoldi’s creative restoration will be highlighted, which is not only the reconstruction of the Basilica but the possibility, through the wire mesh that generates transparency, to understand the monument not only as a historical document but as an artwork that needs to be experienced aesthetically, safeguarding the genius loci, making the site a place to be rediscovered in its link with the territory

Realization of quantum walks with negligible decoherence in waveguide lattices

Quantum random walks are the quantum counterpart of classical random walks, and were recently studied in the context of quantum computation. Physical implementations of quantum walks have only been made in very small scale systems severely limited by decoherence. Here we show that the propagation of photons in waveguide lattices, which have been studied extensively in recent years, are essentially an implementation of quantum walks. Since waveguide lattices are easily constructed at large scales and display negligible decoherence, they can serve as an ideal and versatile experimental playground for the study of quantum walks and quantum algorithms. We experimentally observe quantum walks in large systems (similar to 100 sites) and confirm quantum walks effects which were studied theoretically, including ballistic propagation, disorder, and boundary related effects