# COT 6421 - Homework 3

### Due Monday, February 28

Some more Chapter 5 exercises:
- 5.5
- 5.7
- 5.11 (Hint: Look at problem 5.10.)
- 5.17
- 5.18
- Let REC = {< M > | M is a TM and L(M) is recursive}.
Give two proofs that REC is not r.e.---one that uses
Rice's Theorem II, and one that does not.

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