 where Element: Differentiable {
   /// The viewed array.
   public var base: [Element] {
-    get { return _base }
+    get { _base }
     _modify { yield &_base }
   }
 

    lhs: Array.DifferentiableView,
    rhs: Array.DifferentiableView
  ) -> Array.DifferentiableView {
    precondition(
      lhs.base.count == 0 || rhs.base.count == 0
        || lhs.base.count == rhs.base.count,
      "cannot subtract Array.DifferentiableViews with different counts: "
        + "\(lhs.base.count) and \(rhs.base.count)")
    if lhs.base.count == 0 {
      return rhs
    }
    if rhs.base.count == 0 {
      return lhs
    }
    return Array.DifferentiableView(zip(lhs.base, rhs.base).map(-))
  }


    lhs: Array.DifferentiableView,
    rhs: Array.DifferentiableView
  ) -> Array.DifferentiableView {
    if lhs.base.count == 0 {
      return rhs
    }
    if rhs.base.count == 0 {
      return lhs
    }
    precondition(
      lhs.base.count == rhs.base.count,
      "Count mismatch: \(lhs.base.count) and \(rhs.base.count)")
    return Array.DifferentiableView(zip(lhs.base, rhs.base).map(+))
  }

