theorem Th34:
  A\impA in F
  proof
A1: A\imp((A\impA)\impA)\imp(A\imp(A\impA)\imp(A\impA)) in F by Def38;
A2: A\imp((A\impA)\impA) in F by Def38;
A3: A\imp(A\impA)\imp(A\impA) in F by A1,A2,Def38;
A4: A\imp(A\impA) in F by Def38;
    thus thesis by A3,A4,Def38;
  end;
