An elementary proof of Weyl's limit-classification
Cites background from "An elementary proof of Weyl's limit..."
...Das  showed the existence of the circle equation corresponding to the regular boundary condition (1....
"An elementary proof of Weyl's limit..." refers methods in this paper
...I t should be remarked here tha t this method is not only applicable to any higher even order differential equation, it avoids the whole lot of complications involved in dealing with the singular surfaces t h a t are to be associated wi th higher order equations, as in Everit t ....