Sharp fibers of integral polynomial parameters of degree at most q. The Hilbert multiplicity bounds the field degree by d*q^dimension; a separating integral element gives the same bound for every finite fiber.
theorem
CCDN.bounded_degree_normalization_fiber_card_le
{K : Type u_1}
[Field K]
[CharZero K]
{n m : ℕ}
(I : Ideal (MvPolynomial (Fin n) K))
[I.IsPrime]
(q : ℕ)
(hq : 0 < q)
(l : Fin (m + 1) → MvPolynomial (Fin n) K)
(hl : ∀ (i : Fin (m + 1)), (l i).totalDegree ≤ q)
(hi : Function.Injective ⇑(projectionCoordinateMap I l))
(hint : (projectionCoordinateMap I l).IsIntegral)
(d : ℕ)
(hdimdeg : HasProjectiveDimensionDegree I m d)
(z : Fin (m + 1) → K)
(s : Finset (Fin n → K))
(hzero : ∀ x ∈ s, x ∈ idealZeroLocus I)
(hproj : ∀ x ∈ s, ∀ (i : Fin (m + 1)), (MvPolynomial.eval x) (l i) = z i)
:
The fiber bound for the given normalization, with the function field and degree estimates obtained from the coordinate ring.
theorem
CCDN.linear_normalization_fiber_card_le
{K : Type u_1}
[Field K]
[CharZero K]
{n m : ℕ}
(I : Ideal (MvPolynomial (Fin n) K))
[I.IsPrime]
(l : Fin (m + 1) → MvPolynomial (Fin n) K)
(hl : ∀ (i : Fin (m + 1)), (l i).totalDegree ≤ 1)
(hi : Function.Injective ⇑(projectionCoordinateMap I l))
(hint : (projectionCoordinateMap I l).IsIntegral)
(d : ℕ)
(hdimdeg : HasProjectiveDimensionDegree I m d)
(z : Fin (m + 1) → K)
(s : Finset (Fin n → K))
(hzero : ∀ x ∈ s, x ∈ idealZeroLocus I)
(hproj : ∀ x ∈ s, ∀ (i : Fin (m + 1)), (MvPolynomial.eval x) (l i) = z i)
:
The linear case q = 1 of bounded_degree_normalization_fiber_card_le:
a fiber of a linear normalization has at most d points.