
theorem
  for A,B be transitive with_units non empty AltCatStr, F,F1,F2 be
  covariant Functor of A,B holds F is_naturally_transformable_to F1 & F1
is_naturally_transformable_to F2 implies for t1 being natural_transformation of
F,F1 for t2 being natural_transformation of F1,F2 for a being Object of A holds
  (t2`*`t1)!a = (t2!a)*(t1!a)
by Def5;
