have := normSq_mul a b
a b c : ℤα
⊢ norm (a * b) = norm a * norm b
a b c : ℤα
this :
  ↑normSq (OneHom.toFun (↑↑inclusion) a * OneHom.toFun (↑↑inclusion) b) =
    ↑normSq (OneHom.toFun (↑↑inclusion) a) * ↑normSq (OneHom.toFun (↑↑inclusion) b)
⊢ norm (a * b) = norm a * norm b