Abstract
We present a formalisation of the theory of finite fields, from basic axioms to their classification, both existence and uniqueness, in HOL4 using the notion of subfields. The tools developed are applied to the characterisation of subfields of finite fields, and to the cyclotomic factorisation of polynomials of the form , with coefficients over a finite fields.
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Notes
In this Coq script, at https://github.com/math-comp/math-comp/blob/master/mathcomp/field/finfield.v, Section FinFieldExists.
Here we refer to an element of the multiplicative monoid, for the multiplicative order. Every nonzero field element has the same additive order, as will be discussed in Sect. 3.
For example, in , \(2 * 3 = 0\). Hence in , \((X - 2)(X - 3) = X^2 - 5X = X(X - 5)\), which is an example of a degree 2 polynomial with more than 2 roots.
For example, the integers \(\mathbb {Z}\) form a ring. In , 2X has a leading coefficient not invertible in \(\mathbb {Z}\), hence cannot be taken as a modulus for polynomial division.
Viewing polynomials as functions, this is their function composition.
This proof, based on counting field order elements, is adapted from McEliece [37], Corollary of Theorem 5.7.
Such a proof is given in Justesen and Høholdt [30], Theorem 2.1.2.
This proof works because polynomial rings over a field is a unique factorisation domain, in which irreducibles are primes.
This proof, based on degree and divisibility of special polynomials, is adapted from Belk [12], Theorem 9.
When is not required to be irreducible, is a quotient ring, which becomes a quotient field when is irreducible.
Our proof of this identity follows that given in McEliece [37], Theorem 2.3.
This proof, based on divisibility and pairwise coprime factors, is adapted from Ireland and Rosen [28], Proposition 13.3.2.
Our proof followed the approach given in Herstein [25], Theorem 4.5.11.
Skew fields are fields without the commutative requirement for multiplication, and Wedderburn Theorem asserts that every finite skew field must be commutative, i.e., a field.
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We would like to thank our anonymous referees for their very detailed and constructive feedback.
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Chan, HL., Norrish, M. Classification of Finite Fields with Applications. J Autom Reasoning 63, 667–693 (2019). https://doi.org/10.1007/s10817-018-9485-1
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DOI: https://doi.org/10.1007/s10817-018-9485-1