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Rational profile pairs approach any admissible real rate

Proved
mme_stothers_theorem53_rational_dense_rate

by allychan327 · Sep 10, 2026 · Mathlib 777aaa6 (Lean v4.29.0-rc3)

algebraic-complexityentropylaser-methodmatrix-multiplication

Every rate achievable by a real stationary pair is achievable by an integral one.

Let a,ba, ba,b be strictly positive real ten-class profiles with b∈Nb \in \mathcal Nb∈N and a−b∈Ya - b \in Ya−b∈Y, the two-dimensional kernel of the marginal map spanned by the displayed vectors σ\sigmaσ and τ\tauτ. Then for every

V  <  G(τ,a) E(b)E(a)V \;<\; G(\tau,a)\,\frac{E(b)}{E(a)}V<G(τ,a)E(a)E(b)​

there are strictly positive integral profiles β,β∗\beta, \beta^{*}β,β∗ with the same nine-grade marginals, Qβ∗=QβQ\beta^{*} = Q\betaQβ∗=Qβ, whose normalised partner is again stationary, β∗/D∈N\beta^{*}/D \in \mathcal Nβ∗/D∈N, and which already beat VVV:

V  <  G(τ,β/D) E(β∗/D)E(β/D).V \;<\; G\bigl(\tau, \beta/D\bigr)\,\frac{E(\beta^{*}/D)}{E(\beta/D)} .V<G(τ,β/D)E(β/D)E(β∗/D)​.

The point is that N\mathcal NN is cut out by two binomial relations, b2b72=b4b5b9b_2 b_7^{2} = b_4 b_5 b_9b2​b72​=b4​b5​b9​ and b3b7b8=b4b6b9b_3 b_7 b_8 = b_4 b_6 b_9b3​b7​b8​=b4​b6​b9​, both homogeneous of degree three. Binomial equations are solvable for one variable in terms of the others, so the positive rational points of N\mathcal NN are dense in its positive real points — one approximates eight coordinates freely and defines the remaining two by the relations, which then hold exactly rather than approximately. Homogeneity means no normalisation is needed to stay on N\mathcal NN. Together with the fact that YYY is spanned by two integer vectors, both profiles can be produced directly as integers on a common marginal fibre.

This is what turns the integral form of Theorem 5.3 into the real one: the rate is continuous in the profile on the positive orthant, so a strict inequality at the real pair survives the approximation.

Formalization note. The construction is explicit. At scale nnn one takes ceilings ui=⌈nbi⌉u_i = \lceil n b_i \rceilui​=⌈nbi​⌉ of eight coordinates, multiplies through by u72u8u_7^{2} u_8u72​u8​ to clear denominators, and sets the second and third coordinates to u4u5u9u8u_4u_5u_9u_8u4​u5​u9​u8​ and u4u6u9u7u_4u_6u_9u_7u4​u6​u9​u7​; the two relations then hold as identities in N\mathbb NN. The companion profile is obtained by adding integer multiples of the two kernel vectors, which changes neither the marginals nor the class-weighted total.

Preamble
import Definitions.Def_mme_stothers_general_outer_profile

open MME BigOperators Filter

set_option autoImplicit false
Formal statement
theorem mme_stothers_theorem53_rational_dense_rate
    (tau : ℝ) (a b : Fin 10 → ℝ)
    (hb : MME.StothersFourth.InN b)
    (haPos : ∀ i, 0 < a i) (hbPos : ∀ i, 0 < b i)
    (hsame : MME.StothersFourth.InY (fun i ↦ a i - b i))
    (V : ℝ)
    (hVlt : V < MME.StothersFourth.globalRate 6 tau a a *
      (MME.StothersFourth.entropyProduct b / MME.StothersFourth.entropyProduct a)) :
    ∃ base bstar : Fin 10 → ℕ,
      (∀ r, 0 < base r) ∧ (∀ r, 0 < bstar r) ∧
      (∀ j, MME.StothersFourth.genMarginalBaseCount bstar j =
            MME.StothersFourth.genMarginalBaseCount base j) ∧
      MME.StothersFourth.InN (MME.StothersFourth.genProfileB bstar) ∧
      V < MME.StothersFourth.globalRate 6 tau
            (MME.StothersFourth.genProfileB base)
            (MME.StothersFourth.genProfileB base) *
          (MME.StothersFourth.entropyProduct (MME.StothersFourth.genProfileB bstar) /
            MME.StothersFourth.entropyProduct (MME.StothersFourth.genProfileB base)) := by
  sorry
Source
A. M. Davie and A. J. Stothers, Improved Bound for Complexity of Matrix Multiplication, Proceedings of the Royal Society of Edinburgh A 143(2), 2013, Theorem 5.3, Section 5 (Equation (5.2), its kernel, and the set N) and Section 3, Equations (3.2)-(3.4); https://www.maths.ed.ac.uk/~sandy/a11164.pdf.

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