become especially obvious, when the original equation is regarded as a system of 

 four differential equations of the first order. 



The third step mentioned by Dr. Wasow is essentially an existence proof. 

 Whereas this is usually omitted in applied mathematical research — since the solution 

 constructed carries every conviction of being a uniformly valid solution — Mr. Raben- 

 stein and I are carrying out this proof in view of the fundamental nature of the 

 problem. 



Note added in proof (Nov. 7, 1957). The proof referred to in the above dis- 

 cussions has been completed in the meantime by Rabenstein and myself. A paper is 

 in preparation to give a comprehensive description of the theory. 



371 



