Pierre Boulez turned 70 earlier this year, and it's only apt that one of his disciples is paying homage with a Boulez-esque miniature bearing an enigmatic title. The composer, Philippe Manoury, has long been affiliated with the Institut de Recherche et de Coordination Acoustique/Musique, Boulez's temple of avant-gardism in Paris built and partially subsidized by the French government. His 12-minute tribute, Prelude and Wait, is excerpted from a larger suite for voice and orchestra that's based on Manoury's sketches for an (abandoned) operatic biography of Orson Welles. The prelude, "Prelude of the Magic Night," is a capsule of formal elements from the opera in fast-forward and flashback; its dense texture arises from different takes on a long opening chord. "Wait" steadily builds tension and expectation and ends in a big bang. The music's strategy is straight out of Boulez's Varese-inspired bag of tricks. Also noteworthy on the program is Leon Fleisher, who subs for the ailing Krystian Zimerman in Ravel's Piano Concerto for the Left Hand. Perhaps the best young keyboardist in the 50s and 60s, Fleisher lost the control of his right hand to a mysterious affliction. Reportedly he's regained its use and may resume playing the regular repertoire, though even as a left-handed performer he's astounding. Other works are also classics of modernism: Debussy's Symphonic Fragments From The Martyrdom of Saint Sebastian and Stravinsky's Song of the Nightingale. A preconcert chat with Manoury begins at 7 PM each night. Friday and Saturday, 8 PM, Orchestra Hall, 220 S. Michigan; 435-6666.