Coffee made him feel alert, but also slightly detached -- as always. Neurons were modeled in the greatest detail, and whatever receptors to caffeine and its metabolites had been present on each individual neuron in his original's brain at the time of the scan, his own model-of-a-brain incorporated every one of them -- in a simplified, but functionally equivalent, form.

And the physical reality behind it all? A cubic meter of silent, motionless optical crystal, configured as a cluster of over a billion individual processors, one of a few hundred identical units in a basement vault . . . somewhere on the planet. Paul didn't even know what city he was in; the scan had been made in Sydney, but the model's implementation would have been contracted out by the local node to the lowest bidder at the time.

He took a sharp vegetable knife from the kitchen drawer, and made a shallow cut across his left forearm. He flicked a few drops of blood onto the sink -- and wondered exactly which software was now responsible for the stuff. Would the blood cells die off slowly -- or had they already been surren-dered to the extrasomatic general-physics model, far too unsophisticated to represent them, let alone keep them "alive"?

If he tried to slit his wrists, when exactly would Durham intervene? He gazed at his distorted reflection in the blade. Most likely, his original would let him die, and then run the whole model again from scratch, simply leaving out the knife. He'd rerun all the earlier Copies hundreds of times, tampering with various aspects of their surroundings, trying in vain to find some cheap trick, some distraction which would keep them from wanting to bale out. It was a measure of sheer stubbornness that it had taken him so long to admit defeat and rewrite the rules.

Paul put down the knife. He didn't want to perform that experiment. Not yet.