Indirect proofs
Channel: Douglas Weathers
Date: 2020-05-27

Sometimes proving a fact directly is difficult. However, we can employ some logical sleight of hand -- that contrapositive statements are equivalent -- to help.

MISTAKES: (as always, subtitles are corrected)
1:22 Should be "x and y are not both odd - aka one is even." I don't mean to imply that the negation of "both are odd" is "both are not odd." (DeMorgan's law!)
1:32 "All we said in the proof" should be "theorem" instead, since we have not yet done the proof.

Meant to be watched before or after reading Chapter 4 of the open source textbook Elementary Discrete Mathematics (https://dweathers.github.io/174/book.html).