Representation Matters: An Unexpected Property of Polynomial Rings and its Consequences for Formalizing Abstract Field Theory
Christoph Schwarzweller
DOI: http://dx.doi.org/10.15439/2018F88
Citation: Proceedings of the 2018 Federated Conference on Computer Science and Information Systems, M. Ganzha, L. Maciaszek, M. Paprzycki (eds). ACSIS, Vol. 15, pages 67–72 (2018)
Abstract. In this paper we develop a Mizar formalization of Kronecker's construction, which states that for every field $F$ and irreducible polynomial $p \in F[X]$ there exists a field extension $E$ of $F$ such that $p$ has a root over $E$. It turns out that to prove the correctness of the construction the field $F$ needs to provide a disjointness condition, namely $F \cap F[X] = \emptyset$. Surprisingly this property does not hold for arbitrary representations of a field $F$: We construct for almost every field $F$ another representation $F'$, i.e. an isomorphic copy $F'$ of $F$, not satisfying this condition. As a consequence to $F'$ our formalization of Kro\-necker's construction cannot be applied. All proofs have been carried out in the Mizar system. Based on Mizar's representation of the fields $\mathbb{Z}\_p, \mathbb{Q}$ and $\mathbb{R}$ we also have proven that $\mathbb{Z}\_p \cap \mathbb{Z}\_p[X] = \emptyset$, $\mathbb{Q} \cap \mathbb{Q}[X] = \emptyset$, and $\mathbb{R} \cap \mathbb{R}[X] = \emptyset$ respectively.
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