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Design a DFA for Language: “Containing substring ‘ab’”

= {a, b}

 

Answer:

 

L = {ab, aab, aabb, ……}

 

We can write two regular expressions for the above language:    

But both are equivalent. i.e.,

 

Grammar:

S → bS | aA

A → aA | bB

B → aB | bB | λ

 

Another grammar for RE1

S → Aa | bA

A → aA | bA | λ