# Discussion Notes

I will post notes from each discussion section here.### Discussion 10/04/06

Covers general information, some proofs from previous classes, and hints on homework 1.

### Discussion 10/11/06

Covers hints on homework 2, concatenation and intersection, differences between DFAs and NFAs, and example 1.13/1.15 from the book.

### Discussion 10/18/06

Covers hints on homework 3, and a couple examples of decision procedures.

### Discussion 10/25/06

Covers hints on homework 4, the pumping lemma, and example context-free grammars.

### Discussion 11/01/06

Covers hints on homework 5, the decision procedures we have seen so far, the closure properties we know so far, and an example of using the pumping lemma for CFLs.

### Discussion 11/08/06

Covers hints on homework 6, except for problems 1 and 5. Also goes through a PDA example.

### Discussion 11/15/06

Covers a multi-head Turing machine variant, and decision problems as deciders.

### Discussion 11/22/06

Takes another look at the halting problem, undecidibility, and starts to introduce reduction.

### Discussion 11/29/06

Revists the emptiness and equivalence problems for Turing machines, providing more formal reductions. Also summarizes several of the methods we've seen so far.

### Discussion 12/06/06

Last discussion section. Focuses on proving SUBSET-SUM is NP complete.