ses: you couldn't swap a song from the exuberantly explosive pit-band score of Anyone Can Whistle (1964) with one of the Orientally influenced musical scenes in Pacific Overtures (1976); you couldn't mistake the neurotic pop score of Company (1970) for the elegantly ever-waltzing A Little Night Music (1973). Sondheim hit his stride in the Seventies, forming a unique partnership of hyphenates with Hal Prince: a composer-lyricist and a producer-director working together to re-invent the musical. Some were plotless (Company), some characterless (Pacific Overtures), one went backwards (Merrily We Roll Along). But, as his onetime choreographer Michael Bennett put it, before you can break the rules, you have to know what they are - and Sondheim knows America's cultural heritage better then anybody. Follies (1971) is an affectionate and precise pastiche of Berlin, Kern, Gershwin, Dorothy Fields, Yip Harburg ... Even as he seemed to be turning his back on that great tradition, he was also a glorious summation of it. With Sweeney Todd (1979), the Prince/Sondheim collaboration reached its apogee, blurring the distinctions between lyrics and dialogue, songs and underscoring, and combining a complex plot with operatic emotions to create a unique musical thriller. But their next show, Merrily We Roll Along (1981), flopped, and the two men went their separate ways. Sondheim turned to the author and director James Lapine for Sunday In The Park With George (1984), a work that seemed at times an autobiographical reflection on the problems of making art in a commercial environment. His most recent shows illustrate one of his greatest strengths, hi...