Question 978496
<pre>
 1.  D&#8594;(B&#8594;C)   premise
 2.  B&~C      premise
       conclusion: &#9500; ~D

 3.  (D&B)&#8594;C,    1, Importation
 4.  ~C&#8594;~(D&B)   3, Contrapositive
 5.  ~C          2, Simplification
 6.  ~(D&B)      4,5, Modus Ponens
 7.  ~Dv~B       6, DeMorgan's Law
 8.  B           2, Simplification
 9.  ~~B         8, Double Negation
10.  ~D          7,9, Disjunctive Syllogism 
 
Edwin</pre>