reserve A,B,C for Category,
  F,F1 for Functor of A,B;
reserve o,m for set;
reserve t for natural_transformation of F,F1;

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;
