anchor.diff:  //member _: Elem<'t, 'e, 'p>
   //...
   
  -type [<AbstractClass>] Elem<'t, 'e, 'p> =
  +type [<AbstractClass>] Elem<'t, 'e> =
     new (index) = {Index = index}
   
     /// The index of the element.
  
positive.code: 
    /// Returns the value of the element.
    abstract Get: 't -> 'e
  
  /////////////////////////////////////////////////////////////////////////
  
  
negative.code: /// Representation of a discriminated union type `'u` as nested choices of
  /// type `'c`.
  type [<AbstractClass>] AsChoice<'u, 'c> () = class
    /// 
  //  abstract ToChoice: 'u -> 'c
  
    ///
  //  abstract OfChoice: 'c -> 't
    end
  
  /////////////////////////////////////////////////////////////////////////
  