“…Actually one can prove that M [n] (0, ε) is real for real ε [41], a property which becomes essential to deal with the case in which the nondegeneracy condition a = 0 is not satisfied -see Section 12.2 below. Again the properties (9.1) and (9.4) are proved together, by induction on n: for n = 0 they trivially hold, and, by assuming that they are satisfied up to n − 1, one sees that the series defining M [n] (x, ε) converge, and hence (9.1) can be proved for n; see [42,40,41] for details.…”