Phalanxes of woodwinds, organs, and voices pulse through Philip Glass's most famous opera like nothing so much as a migratory flock engaged in acrobatics overhead. There is no center to the kinetic activity; the down beat might shift, in split-second hindsight, to the up beat, and the synthesizer might suddenly upstage the libretto of nonsense syllables. The exuberant cacophony of overlapping scripts makes the term "counterpoint" seem inadequate, antiquated. Such was Glass's hope, of course, when on the 200th anniversary of the founding of the U.S. he consolidated influences as diverse as raga, minimalism, and progressive rock to produce one of the few canonical works of late-20th-century opera. The title subject might be taken as a pretext for mathematical reverie, but as much as this is "experimental" music; it is a work of art, not science. The ostensible absence of narrative--despite strong voice-over-like recitatives, written in part by the vocalists--is made up for by the lengthy work's dramatic setting, staged by Robert Wilson, and the intense forward momentum of Glass' composition. --Marc Weidenbaum