For each of the items in WP, try to understand why this method is valid (first make sure you know the truth-tables!).

As an example, consider item WP #3 (proof by contradiction). It says that if we want to use "proof by contradiction" to prove some statement "S", then we start by assuming "not S". Then, under this assumption, we try to prove an obviously false statement. Now looking at item WP #1 (Direct proof) this means that we proved "not S ==> false". Now write down the truth-table for "not S ==> false" and you find that that's logically equivalent to "S". Thus, proving "not S ==> false" is equivalent to proving "S".

Next, look at the other items in the WP handout, and see if you can make sense of those too (if not, let me know!).

**Week 3:** Sample questions for test 1. For Friday, work on all
exercises and **turn in: Ex 6 and one of Ex 3,4,5**. If you're not certain that you got Ex 1,2 right, then turn in
one of those too.