The trouble with Leonard Cohen: I'm Your Man, a new documentary featuring excessively singerly performances by Rufus Wainwright, among others, lies in director Lian Lunson's failure to understand that what the Edge calls Cohen's "Biblical authority" emanates from the honoree's unadorned singing voice and only incidentally from his songs. The same problem vitiates most jazz tributes, because so many pantheon figures were defined by their approach to improvisation, not their tunes. Peter Madsen's Prevue of Tomorrow is an exception and then some. It's a salute to 10 left-of-mainstream pianists, living and dead, whosave Lennie Tristano, represented by his line on the chord changes to "Love Me or Leave Me"also qualify as overlooked composers: Mal Waldron, Andrew Hill, Hasaan Ibn Ali, Muhal Richard Abrams, Herbie Nichols, Cecil Taylor, Sun Ra, Randy Weston, and Richard Twardzik. No chameleonand no foolMadsen knows better than to try to emulate each of these mavericks in turn. The point could be that an idiosyncratic piano style is one thing and a composition by an idiosyncratic piano stylist anotherthe latter allows for expansion. Madsen acknowledges the echoes of Hasaan's pounce, Nichols's savior faire, Taylor's percussive arias, Tristano's bass clef rumbles, Hill's italicized lyricism, and so on embedded in these pieceshow could he not? But these echoes never obscure his own technical prowess or improvisatory reach. He's the maverick's maverick, and this could well prove the year's most unlikely tour de force.