I suppose, in introducing Leon Prochnik's The Existentialist, I could pound out a few hundred words on form, draw a parallel or two with earlier works, toss in the names Bunuel and Keaton, render some empty judgment on the film's place in the Cinema of its day; I could do all of those things. I guess. But . . . really, all you need to know about today's offering is this:No film of its time or any other encapsulated so neatly, so lyrically, the attitude lurking in the heart of what used to be known as The New American Cinema.You'll see what I mean.Tom Sutpen