prop_distributivity :: SetOf e s => s -> s -> s -> Bool
prop_distributivity x y z =
  (x `intersection` (y `union` z)) `sameAs`
  ((x `intersection` y) `union` (x `intersection` z))
prop_distributivity :: SetOf e s => s -> s -> s -> Bool
prop_distributivity x y z =
  (x `intersection` (y `union` z)) `sameAs`
  ((x `intersection` y) `union` (x `intersection` z))
prop_distributivity x y z =
  (x `intersection` (y `union` z)) `sameAs`
  ((x `intersection` y) `union` (x `intersection` z))