anchor.diff:  val fromZipper: Zipper<'x> -> 'x
   
   ////////////////////////////////////////////////////////////////////////////////
  -// Heterogenous interface
  +// Heterogeneous interface
   
   val toZipperAny: 'x -> Zipper<'x>
   
  
positive.code: ////////////////////////////////////////////////////////////////////////////////
  // Zipper classes
  
  /// Zipper over type `'w` pointint at any type of hole.
  type [<AbstractClass>] Zipper<'w> =
    abstract DownHeadAny: unit -> option<Zipper<'w>>
    abstract DownHeadThe: unit -> option<Zipper<'w, 'w>>
  
negative.code: val inline prevAny: Zipper<'x> -> option<Zipper<'x>>
  
  ////////////////////////////////////////////////////////////////////////////////
  // Homogeneous interface
  
  val toZipperThe: 'x -> Zipper<'x, 'x>
  
  