效绵鼎 Informal Comments A context-free grammar is a notation for describing languages. ■ It is more powerful than finite automata or RE's, but still cannot define all possible languages. Useful for nested structures,e.g.,parentheses in programming languages 4Informal Comments ◼ A context-free grammar is a notation for describing languages. ◼ It is more powerful than finite automata or RE’s, but still cannot define all possible languages. ◼ Useful for nested structures, e.g., parentheses in programming languages. 4