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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.

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Coherence Spaces and Higher-Order Computation.- Coherence Spaces and Uniform Continuity.- The Free Exponential Modality of Probabilistic Coherence Spaces.- From Qualitative to Quantitative Semantics by Change of Base.- Almost Every Simply Typed Lambda-Term Has a Long Beta-Reduction Sequence.-Algebra and Coalgebra.- Algebra, coalgebra, and minimization in polynomial differential equations.- Equational Theories of Abnormal Termination Based on Kleene Algebra.- Companions, Codensity and Causality.- Nominal Automata with Name Binding.- Games and Automata.- On the existence of weak subgame perfect equilibria.- Optimal Reachability in Divergent Weighted Timed Games.- Bounding Average-energy Games.- Logics of repeating values on data trees and branching counter systems.- Automata, Logic and Formal Languages.- Degree of sequentiality of weighted automata.- Emptiness under isolation and the value problem for hierarchical probabilistic automata.- Partial Derivatives for Context-Free Languages.- Dynamic Complexity of the Dyck Reachability.- Proof Theory.- Cyclic Arithmetic is Equivalent to Peano Arithmetic.- Martin-Lof´s Inductive Definitions are Not Equivalent to Cyclic Proofs.- Probability.- On the relationship between Bisimulation and Trace Equivalence in an Approximate Probabilistic Context.- Computing continuous time Markov chains as transformers of unbounded observation functions.- Pointless Learning.- On Higher-Order Probabilistic Subrecursion. - Concurrency.- A Truly Concurrent Game Model of the Asynchronous -Calculus.- Local Model Checking in a Logic for True Concurrency.- The Paths to Choreography Extraction.- On the Undecidability of Asynchronous Session Subtyping.- Lambda Calculus and Constructive Proof.- A Lambda-Free Higher-Order Recursive Path Order.- Automated Constructivization of Proofs.- Semantics and Category Theory.- A Light Modality for Recursion.- Unifying Guarded and Unguarded Iteration.- Partiality, Revisited: The Partiality Monad as a Quotient Inductive-Inductive Type.- On the Semantics of Intensionality.

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