COMS W3261
Computer Science Theory
Lecture 2: September 10, 2012
Regular Expressions

Outline

1. Review: Operations on Languages

2. Regular Expressions

3. POSIX Regular Expressions

4. Practice Problems

  1. Do the two regular expressions (a+b)* and (a*b*)* denote the same language?
  2. Write a Kleene regular expression for all strings of a's and b's with an even number of a's.
  3. Write a Kleene regular expression for all strings of a's and b's that begin and end with an a.
  4. Write a Posix regular expression that matches all English words ending in dous.
  5. Write a Posix regular expression that matches all English words with the five vowels a,e,i,o,u in order. (The vowels do not have to be next to one another.)

5. References



aho@cs.columbia.edu