3.3-3.5, due January 24

      The most difficult part was understanding proof by contrapositive.  I understand that "if P, then Q" is logically equivalent to "if not Q, then not P."  The confusion come when I try to keep straight which statement I am trying to prove true with a given result.  I am sure that I will understand it better with practice.
      I am impressed by section 3.5 on proof evaluation.  It was not until then that I realized that one proof could prove a variety of results so long as the results are logically equivalent.  Keeping this idea in mind could be particularly useful when employing different techniques to prove results.  It is also useful to be able to think critically about a given proof to determine whether it is a convincing proof or not.