prop_outerGrade x y = 
  (outProd /= 0) ==> grade outProd == grade x + grade y
    where _ :* outProd = x `out` y
prop_outerGrade x y = 
  (outProd /= 0) ==> grade outProd == grade x + grade y
    where _ :* outProd = x `out` y
prop_outerGrade x y = 
  (outProd /= 0) ==> grade outProd == grade x + grade y
    where _ :* outProd = x `out` y