Four of the five men sat frowning because, in conversations with the fifth, time had continually to be allowed for recovering. Then Rowan's eyes brightened and he jumped up. "I take it you mean by that the dress was green all the time," he said, giving a rhetorical answer. "But don't start ringing bells over it," Pendelton said, smiling. "I ought to explain that it had to be green. Not because there's a God, but because it had to. Couldn't be anything else. Except always blue, of course. Always blue, always green, but nothing in between. It rhymes." He shrugged his shoulders. "Because when you change the past, why then you change the past and that includes cameras and film which are often also a part of the past." "Green all the time," Rowan said, looking around at the others. "_Green._" "Green and immaterial!" Pendelton replied. "Green and irrelevant, green and so what! We took the wrong approach. I didn't realize it until I saw Blackburn getting it down on film. Film is part of the past, so it changes. But our _heads_ are also a part of the past. They change too." There was a flash of white teeth against his flushed face as he said: "Depressing, isn't it?" * * * * * "Wait a minute," Shaheen said. "But it's true. The man watching the gargoyles pop out of the Empire State Building _would not have noticed anything_. Quite suddenly the gargoyles would _always_ have been there. The human mind can be toyed with as though it were a piece of film, a coating of silver nitrate crystals on celluloid. It's positively degrading!" "Wait a minute," Shaheen said, pressing his head between his fists. "Something's wrong. You spilled ink on one of that girl's dresses. The blue one apparently." "I spilled ink on a co-temporally-earlier edition of the dress the girl was wearing on Voltaire Mall," Pendelton said, "but can you guarantee she wasn't wearing the green dress to begin with? You can't. Now I'll say this slowly. If you change the past then you can have no memory of what it was before you changed it and therefore you can never prove that you have changed it." He sighed and sat down. "I'd like that to be known as Pendelton's Exclusion Principle." "It's a shame really," Rowan remarked, "you went to an awful lot of trouble." "Well," the president said slowly, "I don't know but that it might be better to keep physics and metaphysics apart after this. Like church and state. Metaphysical questions, after all, are those that don't have answers." A frown passed briefly over Pendelton's countenance. "Wait a minute," he said. "As I recall it, I said something about the wrong approach, I don't remember saying the jig was up. As far as I'm concerned, we've only tried the past so far, we haven't _scratched_ the future. "Take the year 2068 for example," Pendelton said, smiling at them, trying not to sound obnoxious. "If existence is really determined the events of that year are already written down ... sort of."