With the notation of exerc. 2 and the same hypothesis on [x.y] suppose that each of the functions gk is n times differentiable on I; for each function f which is n times differentiable on I, with values in F, put
[g0.f]−[g1.f]′+[g2.f]′′+⋯+(−1)n[gn.f](n)=[h0.f]+[h1.f′]+⋯+[hn.f(n)],
which defines the functions hi (0≤i≤n) without ambiguity (exerc. 2); show that one has
[h0.f]−[h.f]′+[h2.f]′′+⋯+(−1)n[hn.f](n)=[g0.f]+[g1.f′]+⋯+[gn.f(n)]
identically.