Lecture 15

Today:

• 1. Quiz.

  2. Reading question marathon.

  3. Homework 7 solutions.

  4. Homework 8 questions?

For next time:

• 1. Finish Homework 8.

  2. Reading questions below.

Reading questions

Sipser, pages 178-182.

1) What is the difference between M and <M>?

2) What does H do? What does H stand for?

3) What does D do? What does D stand for?

4) Why does the non-existence of D imply the non-existence of H?

5) Why is the complement of a decidable language decidable?

6) What technique is used to prove that if A and A-complement are recognizable, then A is decidable?

7) On page 142, is it clear that if w is in A, then a recognizer for A must halt and accept w; that is, the recognizer can only loop on input that is not in the language?

8) Do exercise 4.2 on page 183: "Consider the problem of determining whether a DFA and a regular expression are equivalent. Express this problem as a language and show that it is decidable."

9) Do exercise 4.3 on page 183, regarding ALL_DFA

10) Do exercise 4.4 on page 183, regarding A ε_CFG