math.AC — Commutative Algebra
Contributed by Darij Grinberg
We show that each univariate polynomial P=p0+p1X+⋯+pmXm∈R[X] over a commutative ring R can be factored into linear factors over a suitable commutative ring extension S of R. The proof proceeds by universal construction: S is defined as the tensor product R⊗CmBm, where Bm is the polynomial ring $\ZZ[a_1, b_1, a_2, b_2, \ldots, a_m, b_m]$, and where Cm is its subring generated by its ``homogenized elementary symmetric polynomials'' Er=∑I⊆[m];∣I∣=r∏i∈Iai∏i∈/Ibi for all 0≤r≤m. The injectivity of the structure homomorphism R→S is deduced from a combinatorial study of the diagonal subring of Bm. In the process, a homogeneous variant of the Garsia--Stanton basis is constructed, and some classical properties of symmetric polynomials are recovered.
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