theorem :: ISOCAT_1:39

for A, B, C, D being Category
for F1, F2 being Functor of A,B
for G1, G2 being Functor of B,C
for H1, H2 being Functor of C,D
for s being natural_transformation of F1,F2
for t being natural_transformation of G1,G2
for u being natural_transformation of H1,H2 st F1 is_naturally_transformable_to F2 & G1 is_naturally_transformable_to G2 & H1 is_naturally_transformable_to H2 holds
u (#) (t (#) s) = (u (#) t) (#) s