LEXICAL ANALYSIS
REGULAR EXPRESSIONS AND FINITE AUTOMATA
Question
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type1


type2


type0


type3

Detailed explanation1: Conclusion: Pushdown automata accepts ContextFree Grammar Language (Type 2) in the Language Hierarchy. The stack in PDA allows it to recognize contextfree languages. Contextfree languages are generated by contextfree grammars, which can be recognized by PDAs.
Detailed explanation2: If a grammar G is contextfree, we can build an equivalent nondeterministic PDA which accepts the language that is produced by the contextfree grammar G.
Detailed explanation3: Basic Structure of PDA A pushdown automaton is a way to implement a contextfree grammar in a similar way we design DFA for a regular grammar. A DFA can remember a finite amount of information, but a PDA can remember an infinite amount of information.
Detailed explanation4: Explanation: Push down automata is for Context free languages and they are termed as Type 2 languages according to Chomsky hierarchy.