Few writers, it seems, are immune to what I call the "Four Friends Formula": take four very different people (women, men, a mix), give them a shared background (often college or university, sometimes an apartment or office), throw in life`s rich pageant, and stir. Voila, a cosmopolitan cocktail (sic) a la Sex and the City. (It doesn`t matter at what stage in her career the author is; Rona Jaffe`s most recent book, THE ROOMMATING SEASON, followed this scenario.) And why not? It offers four different characters, four different storylines, four different perspectives … and more than four ways that things can go wrong.