Durham said, "Do you know what a Garden-of-Eden configuration is?"
Maria was caught blank for a second, then she said, "Yes, of course. In a cellular automaton theory, it's a state of the system that can't be the result of any previous state. No other pattern of cells can give rise to it. If you want a Garden-of-Eden configuration, you have to start with it - you have to put it in by hand as the system's first state."

~ Greg Egan, "Permutation City"