In music, the part of a sonata or fugue that introduces the themes is called the exposition. Merce Cunningham’s choreography, though never created with music in mind, nonetheless looks very musical, and seeing his 1999 BIPED at Annenberg Center Thursday night, it struck me that the piece was an exposition of the bones of ballet.

The first time I saw BIPED, at its 1999 Lincoln Center premiere, I drank in the decor and was dazzled by Paul Kaiser and Shelley Eshkar’s projected animation imagery. The murky, sonarlike thuds of Gavin Bryars’ score and the dancers’ shimmering tourmaline costumes conveyed an underwater impression; the choreography too swam as if under water – and receded, wavery and elusive.

But on second viewing, when the dancers began tracing demilunes with their toes pointed on the floor, I saw what I had not seen the first time – the ghosts of ballet, spare and skeletal. Whether à terre or balancé, the classic rond de jambe was one of the dance’s emerging themes. Deep pliés, unorthodox arabesques, lifts and jetés were a second.

Appearance and disappearance was another theme. The 13 dancers often exited or entered through concealed openings in the backdrop, which swallowed one dancer up after her brief, etchy solo. She emerged momentarily with two other women on each side. Had she been reproduced in quadruple?

Technology also created illusions. Red and blue horizontal stripes floated down the scrim like lines on a page, tracings of motion-captured figures bubbled across it like champagne, diagonal shards of color drifted down like pick-up sticks tossed into a jar of mineral oil. All the while, Aaron Copp’s lighting changed the sense of time, as if the dancing on the ocean floor were illuminated by refracted sunlight.

John King and David Behrman, each of whom has composed for Cunningham, performed Bryars’ 45-minute score live on electric guitar and keyboard. Cellist Loren Dempster, son of the Cunningham collaborator and trombonist Stuart Dempster, also played; at one point, his somber attenuations were shattered by what sounded like a large glass snapping in two.

Some viewers complain that Cunningham’s work lacks emotion. But there is no rapture like that of contemplating pure beauty, and BIPED‘s beauty cannot be overemphasized.

The big buzz of this concert was for eyeSpace, with Mikel Rouse’s 60-minute iPod score International Cloud Atlas, which in its Philadelphia premiere was whittled down to a 20-minute “shuffle.” While some audience members listened to the ambient soundscape created by King and Behrman offstage, most took advantage of the preprogrammed iPods provided.

It was pretty comical to see the electric-blue-clad dancers leaping and lifting to lyrics they could not hear, like “I almost lost my fork” or “Look who’s shopping on the Gaza Strip mall now.” Many in the audience took advantage of the freedom to laugh or make comments, given the feeling of privacy wearing earbuds provided.

Henry Samelson’s gorgeous backdrop was playful too. It looked like a red desert with fireworks bursting from hundreds of prairie dog holes; when the dancers were in upright diagonal positions, they became part of the fiery display.;!category=magazine;&randomOrd=030108031007