museum. "Have I?" he answered, still skeptical. "You have." She ducked her head down into the vehicle and re-appeared, coming out of a door in the side. He was a little surprised at her clothing. He expected something bizarre; at least she might have been dressed in something in keeping with the completely exotic vehicle she was driving. But she was dressed in a simple frock of silk or nylon. Tasteful, modern. She was auburn-haired and very attractive according to Les Ackerman's fastidious standards. "I'm Tansie Lee," she said, offering a slender hand. He took it and found it firm and warm. "I'm Les Ack—" "I know; after all, I've come a long way to find you." "Me?" asked Ackerman in complete wonder. "You don't really know what happened?" Her tone was teasing, and she was obviously enjoying every moment of it. "No, not really," he said. "All I know is that I was bombarding Element X with neutrons and then—well, it's rather hard to describe. I can lean against a tree, but I can also walk through the laboratory door. That doesn't make sense." "Yes it does when you're properly introduced to your environment. Look, Les, you are in the middle, lost territory between two branching streams of events. In one branch, you were the victim of an explosion; in the other, your efforts were successful in the lab. "Now," she said, groping for the right words so that her explanation would be simple, "a tree might be in both worlds; therefore you can lean against it. If a woodcutter in one branch of events cuts the tree down, then you could walk through it in the other branch. The laboratory is there in one branch only; the green bowl of atomic explosion is there in the other. Follow?" Ackerman let that digest for a moment and then said: "What would happen if I tried to break off a tree branch myself?" She laughed. "You'd find—and you'll find—that things consist only of Aristotelian extremes. Either they are non-coincident and therefore very intangible, or you'll find that they are coincident and as untouchable as