∀ {𝕜 : Type u_1} {A : Type u_2} [inst : NontriviallyNormedField 𝕜] [inst_1 : NonUnitalNormedRing A]
  [inst_2 : NormedSpace 𝕜 A] [inst_3 : SMulCommClass 𝕜 A A] [inst_4 : IsScalarTower 𝕜 A A]
  (_x _y : DoubleCentralizer 𝕜 A), (_x * _y).toProdMulOpposite = (_x * _y).toProdMulOpposite