The three hardest questions from exam 1. The first is on wffs, and has application to the new material. The second and third concern validity. Message me in Canvas with any questions, about these or other exam questions.

0:00 Question 14, on wffs and negations
1:43 Identifying the main operator
2:48 Double negations in the proof system, and how to follow the rules (uses rule MT)
5:15 Question 43, on arguments with selfcontradictions for premises
6:41 The truth table test for validity
8:00 Question 8, on validity (the intuitive or Ch 1 explanation)
10:10 An explanation using Ch 8 (uses rule MP)
11:30 What now, after the exam? (Basically, focus on new material, and message me if you have questions)