Scalar System F for Linear-Algebraic λ-Calculus: Towards a Quantum Physical Logic

AbstractThe Linear-Algebraic λ-Calculus [Arrighi, P. and G. Dowek, Linear-algebraic λ-calculus: higher-order, encodings and confluence, Lecture Notes in Computer Science (RTA'08) 5117 (2008), pp. 17–31] extends the λ-calculus with the possibility of making arbitrary linear combinations of terms α.t+β.u. Since one can express fixed points over sums in this calculus, one has a notion of infinities arising, and hence indefinite forms. As a consequence, in order to guarantee the confluence, t−t does not always reduce to 0 – only if t is closed normal. In this paper we provide a System F like type system for the Linear-Algebraic λ-Calculus, which guarantees normalisation and hence no need for such restrictions, t−t always reduces to 0. Moreover this type system keeps track of 'the amount of a type'. As such it can be seen as probabilistic type system, guaranteeing that terms define correct probabilistic functions. It can also be seen as a step along the quest toward a quantum physical logic through the Curry-Howard isomorphism [Sørensen, M. H. and P. Urzyczyn, “Lectures on the Curry-Howard Isomorphism, Volume 149 (Studies in Logic and the Foundations of Mathematics),” Elsevier Science Inc., New York, NY, USA, 2006]