1.

Which of the following regular expressions represents the set of strings which do not contain a substring ‘rt’ if ∑= {r, t}(a) (rt)*(b) (tr)*(c) (r*t*)(d) (t*r*)I got this question in examination.Enquiry is from Building Regular Expressions in section Regular Expressions and Languages of Automata Theory

Answer»

Right CHOICE is (d) (t*r*)

To explain: As Kleene OPERATION is not on the whole of the substring, it will not REPEAT and MAINTAIN the ORDER of t, r.



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