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+5 votes

Which of the following are useful in proving a language to be regular?

- Myhill-Nerode theorem
- Pumping lemma
- Drawing an NFA
- Forming a regular expression

(A) All of these

(B) 1, 3 and 4 only

(C) 2, 3 and 4 only

(D) 3 and 4 only

+10 votes

Best answer

(B)1, 3 and 4 only

As from the given options, Myhill-Nerode theorem is useful by providing necessary and sufficient condition for proving that a language regular. Pumping lemma is often used to prove that a language is **non-regular**. Drawing an NFA can be useful to prove a language is regular. Forming a regular expression can also help us prove if it is a regular language

+2 votes

- The
**Myhill-Nerode theorem**is an important characterization of regular languages. and is is used for regular language. **pumping lemma**is a negativity test and it is used for non regular.- if you
**drow a dfa**. then the language is regular . - if you forming a
**regular expression**.then the language is regular

so option 1,3,4 is right

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