∀ {R : Type u_1} [inst : CommRing R] {M : Type u_2} [inst_1 : AddCommGroup M] [inst_2 : Module R M]
  {Q : QuadraticForm R M} (d₁ d₂ : Module.Dual R M),
  CliffordAlgebra.foldr' Q (CliffordAlgebra.contractLeftAux Q (d₁ + d₂)) ⋯ 0 =
    CliffordAlgebra.foldr' Q (CliffordAlgebra.contractLeftAux Q d₁) ⋯ 0 +
      CliffordAlgebra.foldr' Q (CliffordAlgebra.contractLeftAux Q d₂) ⋯ 0