An Asymptotic Formula for the Iterates of a Function

Let IK be either IR or ? and D an open set of IK containing 0 and starlike with respect to 0 (i.e. an open interval containig 0 in the case IK = IR). If f: D » IK is a continuous function with fixed point 0, then under certain conditions stated below we can prove for the kn- th iterates of f the following asymptotic formula: 1 $$f^{(kn)}bigg({x over n}bigg )=sum_{i-1}^r{1over (nk)^i} f_i(kx)+o bigg({1over n^r}bigg),$$ for n » ∞, k, n and r beeing positive integers and x close enough to 0. The functions f _i are continuous and uniquely determined by f. In particular (1) holds for any function holomorphic on a neighbourhood of zero, having a convergent power series expansion of the form $$f(z)=z+a_2z^2+cdots=sum_{j=1}^infty a_jz^j, a_jin {cal C},a_1=1,$$ and for any integers k, r with r > 0.