DGD3 

Disjunctive normal form:
     * SE Section 1: #7ab (ii)

Solving equivalence problems with truth trees:
    * TT(a):   SE Section 1: #4b (ii)
    * TT(b):   Use truth trees to show that p->q and ¬q -> ¬p are logically equivalent
    * TT(c):   Is the proposition p/\q/\¬r <-> (p->r)/\(q->r) a contradiction? If not, give all counterexamples.