Question 1195752
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4.   R v X           1, DI   (Disjunction Introduction, or "Addition":  if A then certainly "A or B" is also true)
5.  ~(~R • ~X)       4, DeM  (DeMorgan's:  a v b  <==> ~(~a • ~b))
6.  ~K               5,2 MT  (Modus Tollens)
7.  J v Z            6,3 DS  (Disjunctive Syllogism)  
8.  Z v J            7  COMM  (Commutation:  A v B  <==> B v A)