The Lean 4 theorem `phaseFun_add` in the `ChapterShiftedHermiteCore` chapter of the timepiece formalization

import Definitions.Def_ChapterHermiteProductBasis
import Definitions.Def_ChapterHermiteProductCore
import Definitions.Def_ChapterHyperbolicQuadraticEsa
import Definitions.Def_ChapterNavierStokesDifferentialL2
-- Generated from ChapterShiftedHermiteCore.lean — theorem BookProof.ShiftedHermiteCore.phaseFun_add
import Mathlib
import Definitions.Def_ChapterShiftedHermiteCore
import Definitions.Def_ChapterNavierStokesDiffFarisLavine
import Definitions.Def_ChapterShiftedHermiteCore
open BookProof.ShiftedHermiteCore










open MeasureTheory MvPolynomial
open BookProof.HermiteProductCore BookProof.HermiteProductBasis
open BookProof.NavierStokesFlow.DifferentialL2
open BookProof.HyperbolicQuadratic

noncomputable section

variable {d : ℕ}

theorem BookProof.ShiftedHermiteCore.phaseFun_add (k x y : Vd d) : phaseFun k (x + y) = phaseFun k x * phaseFun k y := by sorry