for A, B, C being Category
for F1, G1 being Functor of A,B
for F2, G2 being Functor of A,C st F1 is_transformable_to G1 & F2 is_transformable_to G2 holds
for t1 being transformation of F1,G1
for t2 being transformation of F2,G2
for a being Object of A holds <:t1,t2:> . a = [(t1 . a),(t2 . a)]