eq_circumradius_of_dist_eq — Mathlib

English

Reindexing a simplex by a bijection on indices does not change its circumsphere.

Русский

Перебиндирование индексов симплексa сопряженной биекция не изменяет его circumsphere.

LaTeX

$$$ (s.reindex e).circumsphere = s.circumsphere $ for any equivalence $e$ on index types.$$

Lean4

/-- Given a point in the affine span from which all the points are
equidistant, that distance is the circumradius. -/
theorem eq_circumradius_of_dist_eq {n : ℕ} (s : Simplex ℝ P n) {p : P} (hp : p ∈ affineSpan ℝ (Set.range s.points))
    {r : ℝ} (hr : ∀ i, dist (s.points i) p = r) : r = s.circumradius :=
  by
  have h := s.circumsphere_unique_dist_eq.2 ⟨p, r⟩
  simp only [hp, hr, forall_const, subset_sphere (s := ⟨p, r⟩), Sphere.ext_iff, Set.forall_mem_range, mem_sphere,
    true_and] at h
  exact h.2

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