“…In this section we will assume familiarity with the notions of real, smooth Banach manifolds, smooth maps between (smooth) Banach manifolds, and Banach-Lie groups. As stated at the end of the introduction, the main references concerning the infinitedimensional differential geometry of Banach manifolds and Banach-Lie groups are [1,17,21,45,55], however, we think it is useful to recall here some notions regarding Banach-Lie subgroups of Banach-Lie groups. According to [55, p. 96 and p. 114], every closed subgroup K of a given Banach-Lie group G is a Banach-Lie group with respect to a unique Hausdorff topology in K such that the closed real subalgebra k = {a ∈ g : exp(ta) ∈ K ∀t ∈ R} (171) of the Lie algebra g of G is the Lie algebra of K. In general, the Hausdorff topology on K does not coincide with the relative topology inherited from the norm topology of G. A subgroup K of a Banach-Lie group G which is also a Banach submanifold of G is called a Banach-Lie subgroup of G. In particular, a Banach-Lie subgroup K of G is closed, it is a Banach-Lie group with respect to the relative topology inherited from the topology of G, and its Lie algebra k is given by equation (171) (see [55, p. 128]).…”