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theorem proved term proof

dAlembert_to_ODE_of_contDiff

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formal statement (Lean)

 120theorem dAlembert_to_ODE_of_contDiff
 121    (Hf : ℝ → ℝ)
 122    (h_dAlembert : ∀ t u, Hf (t + u) + Hf (t - u) = 2 * Hf t * Hf u)
 123    (h_diff : ContDiff ℝ 2 Hf)
 124    (h_deriv2_zero : deriv (deriv Hf) 0 = 1) :
 125    ∀ t, deriv (deriv Hf) t = Hf t := by

proof body

Term-mode proof.

 126  intro t
 127  have h_rel := dAlembert_second_deriv_at_zero_of_contDiff Hf h_dAlembert h_diff t
 128  rw [h_deriv2_zero] at h_rel
 129  linarith
 130
 131/-- Bridge from an explicit `ContDiff ℝ 2` hypothesis to the legacy ODE hypothesis. -/

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