for A, B, C being category
for F1, F2 being covariant Functor of A,B
for G1, G2 being covariant Functor of B,C
for t being natural_transformation of F1,F2
for s being natural_transformation of G1,G2 st F1 is_naturally_transformable_to F2 & G1 is_naturally_transformable_to G2 holds
( G1 * F1 is_naturally_transformable_to G2 * F2 & s (#) t is natural_transformation of G1 * F1,G2 * F2 ) by Lm2;