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　　Imagine how much sleep future musicologists will lose over Philip Glass. Throughout his career he has changed his scores to suit the circumstances, trimming them for recordings, for example, because he believes that nonvisual performances benefit from (relative) concision. The notion of an immutable, sacrosanct urtext -- the very thing musicologists sift historical evidence hoping to establish -- is entirely alien to him.
　　Still, you would think that if Mr. Glass held anything sacred, it would be the structure and format of ’’Einstein on the Beach.’’ At that opera’s premiere in 1976, and in its 1984 and 1992 revivals, ’’Einstein’’ played for five hours with no intermission. Free of narrative but rich in associations and imagery -- Einstein as a madly ecstatic violinist but also as the father of nuclear power -- the work unfolded inexorably, its repeated musical phrases creating rhythmic wheels within wheels. The libretto, mostly numbers, solfege syllables and quirky, stream-of-consciousness spoken texts, works its own hypnotic spell. Listeners were free to come and go as they pleased, but some of the work’s power came from its relentlessness, to say nothing of the quirkiness of Robert Wilson’s staging.
　　The version that Mr. Glass and his ensemble presented at Carnegie Hall on Thursday evening swept away the elements that made the work a happening and transformed it into a concert piece: three hours long, with an intermission and with formal seating rules in force. The breadth of the work was presented, if not its full sweep. The two-hour trim was accomplished by deleting sections from all but a few scenes. Some trims were noticeable: Lucinda Childs’s tale of the multicolored bathing cap was intact, as were the quotations from Carole King’s ’’I Feel the Earth Move,’’ but Mr. Bojangles was evicted from this version.
　　Musically, the score survived the trims and might even have benefited from them: The brisker movement from one section to the next highlighted the degree of inventiveness that drives this piece and pointed up passages of real beauty. In ’’Knee Play 3,’’ for example, the unaccompanied chorus sings streams of numbers, yet the music has the grandeur of a sacred setting much of the time and, at others, the energy of a symphonic presto. And Tim Fain, the violinist, gave the solo passages in the second, fourth and fifth ’’Knee Plays’’ and in the climactic, swirling ’’Spaceship Interior’’ scene an electrifying, virtuosic workout.
　　Some of the work’s magic is in the way its elements pull in opposite directions. The repetition of short phrases, on one hand, can be soporific; yet the wheezing keyboard and woodwind textures and the bursts of choral counting, with sibilants creating their own rhythmic patterns, are invigorating. And because the performance is heavily amplified, timbres seem to melt together: Is that repeating fragment a voice, a violin or the top notes of the organ figure?  The ensemble, which included musicians who have been with Mr. Glass from the early days as well as newcomers, gave the score a tight, high-energy readi1．