This book constitutes the proceedings of the 20th International Conference on Foundations of Software Science and Computation Structures, FOSSACS 2017, which took place in Uppsala, Sweden in April 2017, held as Part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2017. The 32 papers presented in this volume were carefully reviewed and selected from 101 submissions. They were organized in topical sections named: coherence spaces and higher-order computation; algebra and coalgebra; games and automata; automata, logic and formal languages; proof theory; probability; concurrency; lambda calculus and constructive proof; and semantics and category theory.

Nominal Game Semantics complements existing introductory literature to game semantics, which highlight the then new structural components necessary to model higher-order computation; for example, arenas, justification pointers, and innocence. In contrast, this monograph focuses on explaining the nominal content of our games. It begins by covering the basics of nominal sets before proceeding to introduce the programming language of study, called GroundML. GroundML is a higher-order language with references capable of storing integers, references to integers, references to references to integers, and so on. Before presenting the game model of GroundML in full detail, the reader is given a flavor of the nominal approach with the presentation of ToyML that, for the sake of simplicity, features only integer-valued references and restricted higher-order types. Because ToyML is simpler, it allows a more direct and elementary presentation of its game semantics, which will help the reader to make a transition to the full-blown model. Nominal Game Semantics has been written in a way that will make it accessible to readers who are familiar with standard denotational semantics and types.