To the perennial question "which comes first, the music or the words?" Ira Gershwin always responded, "the contract." The jest reveals both Ira's consummate professionalism and the self-effacing wit with which he ducked the spotlight whenever possible. Yet the ingeniously inventive melodies George Gershwin composed for such classic songs as "Someone to Watch Over Me," "Embraceable You," "Fascinating Rhythm," "It Ain't Necessarily So," and "Love is...