The Diagonal Problem for Higher-Order Recursion Schemes is Decidable - Clemente, Lorenzo; Parys, Paweł; Salvati, Sylvain; Walukiewicz, Igor (Proceedings of the 31st Annual ACM/IEEE Symposium on Logic in Computer Science, 2016)
Keywords: Theory of computation; Theory of computation -- Formal languages and automata theory; separability problem; downward closure; higher-order recursion schemes; higher-order OI grammars; diagonal problem