Due to an oversight, an error slipped in Section 4.1 of the book, where it is implicitly assumed the case of the Kepler problem. The following text should replace Sections 4.1 and 4.2 of the book. Cross-references may be affected with the new writing. In particular, former crossed references to Eq.(4.3) should now point to current Eq.(4.12). Please find the Erratum below.