In a continuation of the series of papers on integrable systems
where, in 2007, the characteristic function and the motion were
separated in spheroidal coordinates while, in 2008, elliptic
coordinates took the role, the authors describe now a system which,
in the classical case, appears to separate in oblate coordinates.
Remarkably enough, they obtain the pair of hyperbolic and
trigonometric four-term-Hill equations in quantum case.
MR2810758 Gadella, M.; Negro, J.; Nieto, L. M.; Pronko, G. P. Two
charged particles in the plane under a constant perpendicular
magnetic field. Internat. J. Theoret. Phys. 50 (2011), no. 7,
2019--2028. 81Qxx