*Dirk Schlimm*

Due Wednesday, August 2, 2000

- Page 95, Problem 4.

Hand in your answers on a disk (in PC/IBM format). Name your files exactly as it is specified in the problem. - Page 104, Problem 21.

An example for a similar proof is given on page 102 of FOL. Make sure to understand this example before attempting to solve this problem. - Modus tollens: From "A implies B" and "not B" infer "not A".
- Strenghening the antecedent: From "B implies C" infer "(A and B) implies C".
- Weakening the consequent: From "A implies B" infer "A implies (B or C)".

1. Read FOL, pages 91-103 (Sections
4.1-4.4). Do the following problems:

2. Read FOL, page 112 (Section 4.7).

3. Give a *semantic* and a *syntactic* proof
for each of the following valid steps
of reasoning: