Published online by Cambridge University Press: 26 February 2010
Let K be any finite (possibly trivial) extension of ℚ, the field of rational numbers. Let denote the ring of integers of K, and let M ⊆
be a full module in K thus a free ℤ-module of rank [K : ℚ] contained in
; ℤ denoting the ring of rational integers. Regarding
as an abelian group, the index (
: M) is finite. Suppose that m1, …, mk is a ℤ-basis for M and let a ∊
Then the polynomial
(the xi; being indeterminates) will be called a full-norm polynomial; here NK/ℚ denotes the norm mapping from K to ℚ. Apart from constant factors, such a polynomial f(x) is necessarily irreducible in ℤ[x].