Date: Mar 19, 2012 4:51 AM
Author: Ashraf Samhouri
Subject: Tautology Proof Question

Hello guys,

While studying, I've passed through this proof (in the class notes):

Example:
Proof that:
( (p v q) ^ (p -> r) ^ (q -> r) ) -> r
is a tautology?

The solution is:
( (p v q) ^ (¬p v r) ^ (¬q v r) ) -> r
( (p ^ ¬p) v (r ^ q) ^ (¬q v r) ) -> r
(F v (q ^ ¬q) v r) -> r
r -> r
¬r v r
.: T

Actually I can't understand the steps, am not sure if the notes are
well-written here, but I'll appreciate any help in explaining the
proof.

Regards,
ASH