SOLUTION: 1. A -> ~(B v C) 2. ~D -> (~A -> ~E) 3. ~(~E v F) 4. ~F -> (A -> B) /D I don't understand how to do this proof with the conclusion being "D".

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Eval error:

ModPerl::Util::exit: (120000) exit was called at /home/ichudov/project_locations/algebra.com/templates/Algebra/Questions/MoreLikeThis.pm line 159