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Suppose we are given a set V of unknown variables
and a set of polynomial equations C.
By the V-category of C we mean the collection of
polynomial equations p = q of C
such that the set of unknowns appearing in p-q
is exactly V.
That is, p = q is in the V-category of C
if and only if p = q is in C and each element in
V is a variable in p-q and each unknown in p-q belongs to V.
The spreadsheet shown above has three non-empty categories:
a {}-category which equals
{U*U = 1, U U* =1, W*W = 1},
a {x}-category which equals
{x = 0}
and a
{x*}-category which equals
{x* = 0}.
In addition to V-categories,
we shall keep track of the singleton category which
consists of equations of the form
v=p where v is a single variable, p is a polynomial
and
satisfies the technical condition that
v is greater than any of the terms appearing in p with
respect to the monomial order
(see
§).
In the example above, the singleton category consists of
the equations x = 0 and
x*= 0.
These equations are very useful because they say
one unknown can be solved
for
in terms of the others variables
(and therefore eliminated).
Note there is a (harmless) overlap between
the singleton category
and V-categories.
Helton
Wed Jul 3 10:27:42 PDT 1996