Double-Layer Potentials for a Generalized Bi-Axially Symmetric Helmholtz   Equation
  The double-layer potential plays an important r$\hat{\rm o}$le in solving boundary value problems of elliptic equations. Here, in this paper, we aim at introducing and investigating double layer potentials for a generalized bi-axially symmetric Helmholtz equation. By using some properties of one of Appell's hypergeometric functions in two variables, we prove limiting theorems and derive integral equations concerning a denseness of double-layer potentials. 
H. M. Srivastava, Junesang Choi and Anvar Hasanov