Please answer the following question: Information: - In mathematics, computer science, and linguistics, a formal language is a set of strings of symbols together with a set of rules that are specific to it. - Indexed languages are a class of formal languages discovered by Alfred Aho; they are described by indexed grammars and can be recognized by nested stack automata. - Alfred Vaino Aho (born August 9, 1941) is a Canadian computer scientist best known for his work on programming languages, compilers, and related algorithms, and his textbooks on the art and science of computer programming. - Indexed grammars are a generalization of context - free grammars in that nonterminals are equipped with lists of flags , or index symbols . The language produced by an indexed grammar is called an indexed language . - A context-free grammar (CFG) is a term used in formal language theory to describe a certain type of formal grammar. A context-free grammar is a set of production rules that describe all possible strings in a given formal language. Production rules are simple replacements. For example, the rule What is the relationship between 'indexed grammar' and 'formal grammar'?
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