Errata for Discrete Mathematics I.
Last updated 4 December 2011 by Sam Staton
Send me any feedback at sam DOT staton AT cl.cam.ac.uk
Thanks to Thomas Forster, Shaun Hall and others.
Slide 44: (p and not p) is certainly not a tautology! (p or not p) is,
and so is (not (p and not p)).
Slide 54: e <= e' is shorthand for (e < e' or e=e').
Slide 66: Fermat's last theorem should be stated for n>2 (strictly
greater, not greater-than-or-equal).
It is perhaps confusing to say that "Slide 103 is a special case of
the rule on Slide 104."
Slide 104 is generally accepted to be the correct rule for existential
elimination, and that is what we will focus on in this course.
However, in informal practice, outside of structured proof, it is
unusual to use the principle on Slide 104 as it is written. Rather, in
a less formal situation, line m on Slide 104 might be called
"existential instantiation" and you don't bother drawing the box. As
long as the variable name x_1 is totally fresh, then this gives the
principle on Slide 103.