theorem Th14:
  for F being Functor of [:A,B:],C, g being Morphism of A holds F
  ?-dom(g) is_naturally_transformable_to F?-cod(g)
proof
  let F be Functor of [:A,B:],C, g be Morphism of A;
  Hom(dom g,cod g) <> {} by CAT_1:2;
  hence thesis by Th13;
end;
