  We present asymptotically exact solutions of an incommensurate Harper
equation---one-dimensional Schroedinger equation of one particle on a lattice
in a cosine potential. The wave functions can be written as an infinite product
of string polynomials. The roots of these polynomials are solutions of Bethe
equations. They are classified according to the string hypothesis. The string
hypothesis gives asymptotically exact values of roots and reveals the
hierarchical structure of the spectrum of the Harper equation.
