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Example: masses 1,2,3,4,51,2,3,4,51,2,3,4,5 give finitely many normalized central configurations

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AlbouyKaloshin.example_masses_one_to_five

by Lucas · Sep 30, 2026 · Mathlib 0df444a (Lean v4.33.1)

celestial-mechanicscentral-configurationsn-body-problem

For the masses m1=1m_1=1m1​=1, m2=2m_2=2m2​=2, m3=3m_3=3m3​=3, m4=4m_4=4m4​=4, m5=5m_5=5m5​=5, the planar five-body problem has finitely many normalized central configurations: system (4) with n=5n=5n=5 and these masses has finitely many complex solutions.

This is the first explicit 555-tuple of positive masses shown to have finitely many planar central configurations.

Preamble
import Mathlib
import Definitions.Def_AlbouyKaloshin_CentralConfigurations
Formal statement
namespace AlbouyKaloshin

theorem example_masses_one_to_five :
    (NormalizedCC 5 (fun k => ((k : ℕ) + 1 : ℂ))).Finite := by sorry

end AlbouyKaloshin
Source
A. Albouy and V. Kaloshin, Finiteness of central configurations of five bodies in the plane, Annals of Mathematics 176 (2012), no. 1, 535–588, https://doi.org/10.4007/annals.2012.176.1.10, p. 583, Example
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What the Lean code literally says, in plain math · Aristotle (Harmonic)

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Let mk=k+1m_k=k+1mk​=k+1 for k=0,1,2,3,4k=0,1,2,3,4k=0,1,2,3,4 (so the masses are 1,2,3,4,51,2,3,4,51,2,3,4,5, as complex numbers). The set NormalizedCC 5 m is finite: there are finitely many triples (x,y,δ)(x,y,\delta)(x,y,δ) with x,y∈C5x,y\in\mathbb C^5x,y∈C5, δ\deltaδ a symmetric 5×55\times55×5 complex array with zero diagonal, δkl2((xl−xk)2+(yl−yk)2)=1\delta_{kl}^2((x_l-x_k)^2+(y_l-y_k)^2)=1δkl2​((xl​−xk​)2+(yl​−yk​)2)=1 for k≠lk\ne lk=l, xk=∑l≠kmlδkl3(xk−xl)x_k=\sum_{l\ne k}m_l\delta_{kl}^3(x_k-x_l)xk​=∑l=k​ml​δkl3​(xk​−xl​), yk=∑l≠kmlδkl3(yk−yl)y_k=\sum_{l\ne k}m_l\delta_{kl}^3(y_k-y_l)yk​=∑l=k​ml​δkl3​(yk​−yl​) for every kkk, and y1=y0y_1=y_0y1​=y0​.

Human review
  • Endorsed by Shuze Chen · Sep 30, 2026

    Confirmed by the moderator at approval.

  • Endorsed by Lucas · Sep 30, 2026

    Confirmed by the mission captain (proposal self-audit).

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