ABSTRACT. In Mozart's Fantasy in C minor, K. 475, Sigerson notes, the Lydian interval represents the minimum action required to move into the domain of multiply-connected, polyphonic vocal registration. Pechenuk argues that Mozart concentrated in his Ave verum all the momentous discoveries he had made over the preceding decade. Libin says that Mozart, the "consummate improviser", probably did not limit his improvisatory impulse to a few discrete closing areas, or to the addition of ornamentation here and there.