How do you go about writing a single story with two or more authors? There are some wonderful stories out there with more than one author. Some appear absolutely seamless, with no perceptible differences in style and approach. I can think of one marvelous example in the Archive written by four people, each of whom kept his own voice, yet the story works wonderfully as a unified whole. How do you do it? Where do you begin? How do you decide on the story arc, the characters, and all that? How do you decide who contributes what? How do you pull it all together?