ABSTRACT
The modes un = ipnexp(iy/Xnx), or un = tpnQxp(—iy/X^x), are called propagating to the right, or left, respectively, if \n > 0 and damping if Xn < 0. Let A+ = {\n\Im\f\n > 0}. It is well known that the unique solution of the problem (l)-(4) can be found only under some additional conditions, i.e.
