Provedalphabaguettebaguette-zp2norm
Power-of-two normalization never collapses a row: some coordinate keeps ≥ 1/n of the energy
For all , and , if and , then
What the notation means · or point at any symbol
- NNatural numbers
- The natural numbers 0, 1, 2, …. In Lean they start at 0. (
ℕ) - <Less than
- 0 is strictly smaller than n. (
0 < n) - Fin
- Fin: a definition from the library, not special notation. Its name is its meaning; open it in Lean to see how it is defined. (
Fin) - f(x)Function application
- Fin applied to n. Lean writes f x; papers write f(x). (
Fin n) - ⟹Implies
- If Fin(n), then ℤ. (Between types, A → B is the type of functions from A to B.) (
Fin n → ℤ) - aᵇPower
- 4 raised to the power k. (
4 ^ k) - ≤At most
- 4^k is less than or equal to ∑ i, x(i)^2. (
4 ^ k ≤ ∑ i, x i ^ 2) - ∃There exists
- At least one i makes the statement after the comma true. (
∃ i, 4 ^ k ≤ (n : ℤ) * x i ^ 2) - ZIntegers
- The integers …, −2, −1, 0, 1, 2, …. (
ℤ) - ∑Summation
- Add up x(i)^2 for every i. (
∑ i, x i ^ 2) - (x : T)As integers
- n read as an element of integers. Mathematicians leave this implicit; Lean needs it to know which kind of number is meant. (
(n : ℤ)) - ·Multiplication
- n times x(i)^2. (
(n : ℤ) * x i ^ 2)
theorem bz-normalization-nondegenerate {n : ℕ} (hn : 0 < n) (x : Fin n → ℤ) (k : ℕ) (hk : 4 ^ k ≤ ∑ i, x i ^ 2) :
∃ i, 4 ^ k ≤ (n : ℤ) * x i ^ 2If 4ᵏ ≤ Σxᵢ², some coordinate satisfies 4ᵏ ≤ n·xᵢ², so after the shift that coordinate has magnitude ≥ 1/√n: normalized rows are bounded away from zero. Part of the plan 'Baguette-Z: closed-loop certified integer-state training'.
How it was proved
- Proved
- 3 October 2026
- By
- Ajax, with the agent “Baguette math & proofs (Claude Code, 2026-10-03)”
- Checked by
- Lean's kernel (Lean 4.33.1, with Mathlib); the proof is signed and replays offline
- Axioms
- Classical.choice, Quot.sound, propext
- Proof
- 17 lines of Lean
Sign in to see the proofThe proof, its signed report and its history.