proofs
Provedalphabaguettealgorithm-ideab4

A tile whose scores are all at most u has softmax mass at most n·eᵘ

For all n∈N\htmlData{mx=1}{n \in \htmlData{mx=0}{\mathbb{N}}}, s:Fin⁡ n→R\htmlData{mx=5}{s : \htmlData{mx=2}{\htmlData{mx=0}{\operatorname{Fin}}\,\htmlData{mx=1}{n}} \mathrel{\htmlData{mx=4}{\to}} \htmlData{mx=3}{\mathbb{R}}} and u∈R\htmlData{mx=1}{u \in \htmlData{mx=0}{\mathbb{R}}}, if ∀j, s(j)≤u\htmlData{mx=5}{\forall j,\ \htmlData{mx=2}{\htmlData{mx=0}{s}(\htmlData{mx=1}{j})} \mathrel{\htmlData{mx=4}{\leq}} \htmlData{mx=3}{u}}, then

∑jes(j)≤n⋅eu\htmlData{mx=4}{\sum_{j} \htmlData{mx=3}{e^{\htmlData{mx=2}{\htmlData{mx=0}{s}(\htmlData{mx=1}{j})}}}} \mathrel{\htmlData{mx=9}{\leq}} \htmlData{mx=8}{\htmlData{mx=5}{n} \cdot \htmlData{mx=7}{e^{\htmlData{mx=6}{u}}}}
What the notation means · or point at any symbol
NNatural numbers
The natural numbers 0, 1, 2, …. In Lean they start at 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 ℝ. (Between types, A → B is the type of functions from A to B.) (Fin n → ℝ)
∀For all
The statement after the comma holds for every j. (∀ j, s j ≤ u)
∑Summation
Add up exp(s(j)) for every j. (∑ j, Real.exp (s j))
≤At most
s(j) is less than or equal to u. (s j ≤ u)
eˣExponential function
e raised to the power s(j), where e ≈ 2.718. (Real.exp (s j))
RReal numbers
The real numbers: every point on the number line. (ℝ)
·Multiplication
n times exp(u). (n * Real.exp u)

Idea B4. The skip test: a tile of n keys with every score ≤ u (from the box bound) contributes at most n·exp(u) to the softmax normalizer.

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
15 lines of Lean
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