Key points are not available for this paper at this time.
Our essential results and methods have already been published in two preliminary notes('). Basically, our procedure consists in an application of the Riquier theory of systems of partial differential equations to a certain linear differential system e on which the inverse problem can be made to depend. This differential system has already appeared-derived in a different way-in the interesting work, of little more than a decade ago, by D. R. Davis on the inverse problem(2); but, as he stated, its general solution-even existence-theoreticallypresented difficulties which he could not overcome.
Jesse Douglas (Wed,) studied this question.