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theorem proved term proof

differentiableAt_coordRay_spatialNormSq

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formal statement (Lean)

 409theorem differentiableAt_coordRay_spatialNormSq (x : Fin 4 → ℝ) (μ : Fin 4) :
 410    DifferentiableAt ℝ (fun t => spatialNormSq (coordRay x μ t)) 0 := by

proof body

Term-mode proof.

 411  unfold spatialNormSq
 412  apply DifferentiableAt.add
 413  · apply DifferentiableAt.add
 414    · exact differentiableAt_coordRay_i_sq x μ 1
 415    · exact differentiableAt_coordRay_i_sq x μ 2
 416  · exact differentiableAt_coordRay_i_sq x μ 3
 417
 418/-- Differentiability of spatialRadius along a coordinate ray. -/

used by (3)

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depends on (9)

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