We study some properties of tau-functions of an isomonodromic deformation leading to the fifth Painleve equation. In particular, here is given an elementary proof of Miwas formula for the logarithmic differential of a tau-function.
We propose an analytic proof of the Malgrange-Sibuya theorem concerning a sufficient condition of the convergence of a formal power series satisfying an ordinary differential equation. The proof is based on the majorant method and allows to estimate the radius of convergence of such a series.
