theorem Th201:
  A\impB in F & A\impC in F implies A\imp(B\andC) in F
  proof
    assume Z0: A\impB in F & A\impC in F;
    (A\impB)\imp((A\impC)\imp(A\imp(B\andC))) in F by Th49;
    then (A\impC)\imp(A\imp(B\andC)) in F by Z0,Def38;
    hence A\impB\andC in F by Z0,Def38;
  end;
