   _precondition(
     newElementIndex == newElementsEndIndex,
     "Cannot replace a slice of a MutableCollection with a slice of a smaller size")
-  */
 }
 
 @available(*, unavailable, renamed: "MutableCollection")

  }
}

// TODO: swift-3-indexing-model - review the following
internal func _writeBackMutableSlice<
  C : MutableCollection,
  Slice_ : Collection

    newElementIndex != newElementsEndIndex {

    self_[selfElementIndex] = slice[newElementIndex]
    self_.successor(updating: &selfElementIndex)
    slice.successor(updating: &newElementIndex)
  }

  _precondition(
