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One natural operation is called SmallBasis. We begin by describing an
idealized version of it.
SmallBasis associates to
a finite sequence ,
a subset *Y* of *X* such that
if and only if
.
for each
.
Note that *SmallBasis*(*X*) depends on the order of the 's
in the sequence *X*.

The reason that SmallBasis cannot be fully implemented
on a computer is that one cannot in general decide
whether or not
.

*Helton *

Wed Jul 3 10:27:42 PDT 1996