Separation of Variables and Contractions on Two-Dimensional Hyperboloid
  In this paper analytic contractions have been established in the $R\to\infty$ contraction limit for exactly solvable basis functions of the Helmholtz equation on the two-dimensional two-sheeted hyperboloid. As a consequence we present some new asymptotic formulae. 
Ernie Kalnins, George S. Pogosyan and Alexander Yakhno
math-ph math.MP nlin.SI