for A, B, C being category
for F1 being covariant Functor of A,B
for G1, G2 being covariant Functor of B,C
for f being natural_equivalence of G1,G2 st G1,G2 are_naturally_equivalent holds
( G1 * F1,G2 * F1 are_naturally_equivalent & f * F1 is natural_equivalence of G1 * F1,G2 * F1 )