An interesting coupled-anharmonic-oscillator extension of the
coupled-harmonic-oscillator results of previous paper [16] where a
class of special non-Hermitian 2D models solvable by Bogoliubov
transformation has been considered at the ``excluded'' values of
couplings at which the Bogoliubov transformation ceases to exist. In
spite of the loss of separability and of the diagonalizability of
the resulting pseudo-Hermitian model, its shape invariance and the
equidistance of the spectrum is shown to imply the feasibility of
the construction of the eigenfunctions as well as of the associated
functions.

MR2950286 Cannata, F.; Ioffe, M. V.; Nishnianidze, D. N.
Equidistance of the complex two-dimensional anharmonic oscillator
spectrum: the exact solution. J. Phys. A 45 (2012), no. 29, 295303,
11 pp. 81Qxx