On the Stokes matrix for a family of infinitely degenerate operators of second order (Q1607208)

This paper concerns infinitely degenerate operators of the type \[ D^2_t u+ \lambda(t)^2 e^{2i\varphi} D^2_x u- b(t) e^{i\varphi} D_x u. \] In terms of the Stokes matrix, sufficient conditions for the operator to be hypoelliptic and locally solvable at \((0,0)\) are given.