`BookProof.ChapterOrthogonalSums.hasSum_smul_of_hasSum_norm_sq` [CompleteSpace E] {ι : Type*} {v : ι → E} (hv : Orthonormal ℂ v) {y : E} (h : HasSum (fun k => ‖⟪v k, y⟫_ℂ‖ ^ 2) (‖y

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`BookProof.ChapterOrthogonalSums.hasSum_smul_of_hasSum_norm_sq` [CompleteSpace E] {ι : Type*} {v : ι → E} (hv : Orthonormal ℂ v) {y : E} (h : HasSum (fun k => ‖⟪v k, y⟫_ℂ‖ ^ 2) (‖y · Prove2Me