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Joined 2026-09-21 Message
Incoming links: Closure of context-free languages under concatenation
Past exam of the mathematics course of the University of Cambridge 2019 ii Paper 1 4H c Solution Created 2026-09-24 Updated 2026-10-03
Take context-free grammars for and rename their nonterminals so that they are disjoint. If their start symbols are , add a new start symbol and the productionAll productions remain context-free. A derivation from produces a word from followed by a word from , and every such concatenation has a derivation. Thus the new grammar generates , proving closure of context-free languages under concatenation.