The theory says that these default-hierarchy models ought to emerge whether the principles are implemented as a classifier system or in some other way, says Holland. (In fact, many of the computer simulations quoted in Induction were done with PI, a somewhat more conventional rule-based program devised by Thagard and Holyoak.) Nonetheless, he says, it was thrilling to see the hierarchies actually emerge in Goldberg’s pipeline simulation. The classifier system had started with nothing. Its initial set of rules had been totally random, the computer equivalent of primordial chaos. And yet, here
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