Constructing a universe for the setoid model -- Nominal Equational Problems -- Finding Cut-Offs in Leaderless Rendez-Vous Protocols is Easy -- Fixpoint Theory - Upside Down -- "Most of"' leads to undecidability: Failure of adding frequencies to LTL -- Combining Semilattices and Semimodules -- One-way Resynchronizability of Word Transducers -- Fair Refinement for Asynchronous Session Types -- Running Time Analysis of Broadcast Consensus Protocols -- Leafy automata for higher-order concurrency -- Factorization in Call-by-Name and Call-by-Value Calculi via Linear Logic -- Generalized Bounded Linear Logic and its Categorical Semantics -- Focused Proof-search in the Logic of Bunched Implications -- Interpolation and Amalgamation for Arrays with MaxDi -- Adjoint Reactive GUI Programming -- On the Expressiveness of Büchi Arithmetic -- Parametricity for Primitive Nested Types -- The Spirit of Node Replication -- Nondeterministic and co-Nondeterministic Implies Deterministic, for Data Languages -- CertifyingInexpressibility -- A General Semantic Construction of Dependent Re nement Type Systems, Categorically -- Simple Stochastic Games with Almost-Sure Energy-Parity Objectives are in NP and coNP -- Nondeterministic Syntactic Complexity -- A String Diagrammatic Axiomatisation of Finite-State Automata -- Work-sensitive Dynamic Complexity of Formal Languages -- Learning Pomset Automata -- The Structure of Sum-Over-Paths, its Consequences, and Completeness for Clifford -- A Quantified Coalgebraic van Benthem Theorem.

Open Access

This open access book constitutes the proceedings of the 24th International Conference on Foundations of Software Science and Computational Structures, FOSSACS 2021, which was held during March 27 until April 1, 2021, as part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2021. The conference was planned to take place in Luxembourg and changed to an online format due to the COVID-19 pandemic. The 28 regular papers presented in this volume were carefully reviewed and selected from 88 submissions. They deal with research on theories and methods to support the analysis, integration, synthesis, transformation, and verification of programs and software systems. .