On the theory of infinite systems of differential equations and their application to the theory of stochastic processes and the perturbation theory of quantum mechanics

Arley (I943) ~ 2.2--2.6 and chap. 7. We shall in the following tacitly assume x to be real, but the proofs are also valid in ease x varies on a regular curve L without double points in the complex plane, if, only, we interpret I x--xo[ as the length of the curve L from x o to x. a well-known theorem from the theory of analytic functions. Using this theoreL,