Question

Give the regular expressions of the following languages (alphabet is ab):

a. {w | w has a length of at least three and its second symbol is a b}

b. {w | w begins with an a and ends with a b}

c. {w | w contains a single b}

d. {w | w contains at least three a's}

e. {w | w contains the substring baba}

d. {w | w is a string of even length}

e. The empty string

f. The empty language

Answer 1

a) (a+b) * b (a+b) *

b) a (a+b) * ab

C) a* b a*

d) (a+b) * aaa (a+b) *

e) (a+b)*(abba)(a+b)*

F) (aa + bb +ba +ab) *