theorem Th34:
  for F1,G1 being Functor of A,B, F2,G2 being Functor of A,C st F1
  is_transformable_to G1 & F2 is_transformable_to G2 holds <:F1,F2:>
  is_transformable_to <:G1,G2:>
by Lm3;
