When analyzing individual gates in circuitry, one usually assumes that
inputs are either 0 or 1, as are the outputs, but the fact is that th
ese input values are really either ''high'' voltage or ''low'' voltage
. Determining whether or not a given input is to be considered as high
or low depends on a physical measurement of the voltage. Since physic
al measurement is never exact, it is more realistic to consider ''high
,'' ''low,'' and ''indeterminate,'' hence considering three possible v
alues, rather than two, when reasoning about computer hardware. When c
onsidering physical measurement as part of the determination as to wha
t inputs and outputs are for a given gate, one can no longer reason ab
out these gates using boolean logic. There are several possible non-bo
olean alternatives one may consider. We will examine motivation for so
me such alternatives and point out how we might apply them to a partic
ular model of computation: the billiard ball model. (C) 1998 Elsevier
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