4.5 Method for Using Now

For a skeleton demonstration, now is sometimes used to demonstrate not p. Now is used as follows:

      now assume p;
         ······
         ······
       thus contradiction;
      end;

    With now ∼ end, now is considered as one sentence (logical formula). This now ∼ end is the same with not p. Or, with assume p, it becomes a logical formula p that implies a contradiction.