proofs
Provedalphabaguettebaguette-zp2norm

Power-of-two normalization never collapses a row: some coordinate keeps ≥ 1/n of the energy

For all n∈N\htmlData{mx=1}{n \in \htmlData{mx=0}{\mathbb{N}}}, x:Fin⁡ n→Z\htmlData{mx=5}{x : \htmlData{mx=2}{\htmlData{mx=0}{\operatorname{Fin}}\,\htmlData{mx=1}{n}} \mathrel{\htmlData{mx=4}{\to}} \htmlData{mx=3}{\mathbb{Z}}} and k∈N\htmlData{mx=1}{k \in \htmlData{mx=0}{\mathbb{N}}}, if 0<n0 \mathrel{\htmlData{mx=1}{<}} \htmlData{mx=0}{n} and 4k≤∑ix(i)2\htmlData{mx=1}{4^{\htmlData{mx=0}{k}}} \mathrel{\htmlData{mx=7}{\leq}} \htmlData{mx=6}{\sum_{i} \htmlData{mx=5}{\htmlData{mx=4}{\htmlData{mx=2}{x}(\htmlData{mx=3}{i})}^{2}}}, then

∃i, 4k≤n⋅x(i)2\htmlData{mx=10}{\exists i,\ \htmlData{mx=1}{4^{\htmlData{mx=0}{k}}} \mathrel{\htmlData{mx=9}{\leq}} \htmlData{mx=8}{\htmlData{mx=3}{\htmlData{mx=2}{n}} \cdot \htmlData{mx=7}{\htmlData{mx=6}{\htmlData{mx=4}{x}(\htmlData{mx=5}{i})}^{2}}}}
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)

If 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.

More proved statements