Question 199553
Note: I'm going to use "<->" for "if and only if" and "*" for "and"


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1.   B <-> W
2.   L -> B
3.   ~B v ~W           :.  ~(W v L)
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4.   (B -> W) * (W -> B)             1      Material Equivalence
5.   (W -> B) * (B -> W)             4      Commutation
6.   B -> W                          4      Simplification
7.   W -> B                          5      Simplification
8.   B -> ~W                         3      Material Implication
9.   W -> ~W                       7,8      Hypothetical Syllogism
10.   ~W v ~W                        9      Material Implication
11.  ~W                             10      Tautology
12.  ~B                           6,11      Modus Tollens
13.  ~L                           2,12      Modus Tollens
14.  ~W * ~L                     11,13      Conjunction 
15.  ~(W v L)                       14      De Morgan's Law
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