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2.5. THE BUCHBERGER ALGORITHM 23<br />

(ii) each p ∈ G is completely reduced modulo G −{p}.<br />

Theorem 2.22. Every polynomial ideal I (not equal <strong>to</strong> {0}) has a unique reduced<br />

Gröbner basis with respect <strong>to</strong> a monomial ordering.<br />

For a proof see Proposition 6 of §2.7 of [28].<br />

Example 2.12 (continued). A reduced Gröbner basis for the ideal I = 〈f 1 ,f 2 〉 =<br />

〈x 2 − 2y 2 ,xy− 3〉 is G ′′ = {x − 2 3 y3 ,y 4 − 9 2 }.<br />

The Buchberger algorithm yields a method <strong>to</strong> solve the ‘ideal equality problem’:<br />

two ideals I 1 and I 2 have the same reduced Gröbner basis if and only if they are equal.<br />

There are many improvements which have been made <strong>to</strong> this basic Buchberger<br />

algorithm in the last decades, i.e., yielding the Refined Buchberger Algorithm or<br />

the Faugère F4 Algorithm. Improvements are mostly aimed at avoiding redundancy<br />

in the set of genera<strong>to</strong>rs of the Gröbner basis or involving variations in efficiently<br />

selecting a pair {p, q} ∈M. Other improvements are based on predicting a-priori<br />

reductions of the S-polynomial which yield a zero solution. These reductions can then<br />

be discarded. Despite all the improvements made <strong>to</strong> the basic Buchberger Algorithm<br />

it is still computational very demanding because a Gröbner basis can be very large.<br />

In fact, it can be much larger than the initial set of polynomials. For state-of-the-art<br />

implementations of the Buchberger algorithm the reader may wish <strong>to</strong> consult Chapter<br />

5.5 of [10] and [44].

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