“…It is easy to see that B × ⊆ KAN; hence g = kb ∈ KAN = m(K × A × N ). The fact that K, A, N are Banach-Lie groups with the corresponding Lie algebras k, a, and n, respectively, follows for instance by Corollary 3.7 in [Be06], and in addition the inclusion maps of K, A, and N into G are smooth. It then follows that the multiplication map m : K × A × N → G is smooth as well.…”