Formal Language & Automata Theory Shyamanta M Hazarika Computer Sc. & Engineering Tezpur University http://www.tezu.ernet.in/~smh
Regular Languages Regular languages are closed under: Union Concatenation Star operation
Regular Languages Namely, for regular languages and : Union Concatenation Star operation Regular Languages
We will prove Regular languages are closed under: Complement Intersection
We will prove Namely, for regular languages and : Complement Regular Intersection Regular Languages
Complement Theorem: For regular language the complement is regular
Complement Theorem: For regular language the complement is regular Proof: Take DFA that accepts and make nonfinal states final final states nonfinal Resulting DFA accepts
Example
Intersection Theorem: For regular languages and the intersection is regular
Intersection Theorem: For regular languages and the intersection is regular Proof: Apply DeMorgan’s Law:
Intersection regular regular regular regular regular
Standard Representations of Regular Languages DFAs Regular Grammars NFAs Regular Expressions