Question

Which of the following is not a regular expression?

(a) [(a+b)*-(aa+bb)]*

(b) [(0+1)-(0b+a1)*(a+b)]*

(c) (01+11+10)*

(d) (1+2+0)*(1+2)*

This question was addressed to me in my homework.

Origin of the question is Regular Grammar topic in chapter Contextfree Grammar and Syntax Analysis of Compiler

Answer 1

The correct choice is (b) [(0+1)-(0b+a1)*(a+b)]*

Best explanation: Except [(0+1)-(0b+a1)*(a+b)]* all are regular expression.