Remember Phillipe Petit, the aerialist? Well, for argument's sake, let's assume that Scott Fitzgerald and Ernest Hemingway represent, in terms of modern American prose fiction, the twin towers of the World Trade Center--and Professor Bruccoli, in this his sixteenth project concerning one or the other, the guy who checks the soundness of the tightrope stretched between them. With the aid of liberal paraphrase of Hemingway's as yet unpublished letters, Bruccoli does basically a paste-and-scissors job, with little psychological felicity and no critical ambition, of establishing the uneasy friendship between these two big boys. Hemingway comes off again and again as exactly what Carlos Baker concluded: he was a bully, an exaggerator, insecure, waspish; one of his letters to Fitzgerald is signed ""Ernest M. Shit."" Amen. And Fitzgerald? Overgenerous, a glutton for punishment, flaws the size of trenches, heartbreaking serf-knowledge and a talent so graceful, just, and natural as to beg to be maligned. Of interest here is the evidence of the careful (and hardly appreciated though often followed) advice Fitzgerald gave Hemingway on the latter's working drafts; though Hemingway writes to Maxwell Perkins that ""Scott could never think,"" contrary proof is abundant here. Not only could Fitzgerald think, he also could know; ""His inclination,"" he writes in a late letter concerning Hemingway, ""is toward megalomania and mine toward melancholy."" That about says it, according to all the facts corralled by Bruccoli on this the most cruel and hopeless literary friendship since Rimbaud and Verlaine.