I.   Write solutions to the following problems:

           A.   Derive (P v Q) <-> (P & Q) from

               1.   P -> Q                  Premise
               2.   P                       Premise

           B.   Derive P -> (P -> (P & Q)) from

               1.   P -> Q                  Premise

           C.   Without using Trans., derive (P -> Q) <-> (~Q -> ~P) from
                scratch.

           D.   Consider the following argument:

               1.   P -> Q                  Premise
               2.   ~P v Q                  1, Impl.
               3.   (~P v ~P) v Q           2, Taut.
               4.   ~P v (~P v Q)           3, Assoc.
               5.   P -> (~P v Q)           4, Impl.
               6.   P -> (P -> Q)           5, Impl.

                Write a 4-line proof in which you derive the conclusion of
                this proof from its premise by using CP--instead of the way
                I derived it here.