CMPSCI 401: Theory of Computation

David Mix Barrington

Spring, 2011

Questions and Answers on Homework Assignment #2

HW#3 is due on paper in class, Monday 14 February 2011

Question text is in black, my answers in blue.

• Question 2.1, posted 12 February: Problem B-1 refers to Exercise 1.6(l). In the solutions handed out for that Exercise (which was on HW#1), the diagram is missing a 1-loop on state q1d.

  You are right, thanks for catching the mistake.

• Question 2.2, posted 12 February: I think there is a similar problem in the solution to Exercise 1.10 (a) in HW#1 -- I don't see how this NFA accepts 1111, which does have at least three ones. Shouldn't we add a 1-loop on state q5?

  Yes, you need to add that loop for the NFA to be correct. Thanks for catching the mistake. Note that 1.10 (a) asks for an NFA for the star of the language of 1.6 (b), not for that language itself -- this explains the ε-move from q5 to q2.

  Last modified 12 February 2011