Let G be a connected Lie group and φ an analytic linear representation of G on a complete normable space E. Let E1,E2 be two closed vector subspaces of E such that E2⊂E1. The following conditions are equivalent:
(i) φ(g)x≡x(modE2) for all g∈G and all x∈E1; (ii) L(φ)(L(G)) maps E1 into E2.
⇔⇔φ(g)x≡x(mod E2)for all g∈G and all x∈E1φ(expa)x≡x(mod E2)for all a∈L(G) and all x∈E1(expL(φ)a)x≡x(mod E2)for all a∈L(G) and all x∈E1.
On the other hand, if u∈L(E), then
⇔exp(λu)x≡x(mod E2)for all λ∈K and all x∈E1u(E1)⊂E2
whence the proposition.
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.