In many Western styles, it is desirable to find efficient, independent voice leadings
between transpositionally or inversionally related chords. The progressions in Fig. 1 are all
of this type (Movie S3). A chord can participate in such progressions only if it is nearly
symmetrical under transposition, permutation, or inversion (16). I conclude by describing
these symmetries, explaining how they are embodied in the orbifolds’ geometry, and
showing how they have been exploited by Western composers.