anchor.diff:  #endif
     val inline delay: (unit -> #Job<Cons<'x>>) -> Stream<'x>
   
  -  /// A choice stream that never produces any values and never closes.
  +  /// A choice stream that never produces any values and never closes.  While
  +  /// perhaps rarely used, this is theoretically important as the identity
  +  /// element for the `switch` and `amb` combinators.
     val inline never<'x> : Stream<'x>
   
     /// Constructs a choice stream that is closed with an error.
  
positive.code:   ///
    /// While the most common operations are very easy to implement on choice
    /// streams, some operations perhaps require more intricate programming than
    /// with push based models.  For example, `groupByFun` and `shift`, that
    /// corresponds to `Delay` in Rx, are non-trivial, although both
    /// implementations are actually much shorter than their .Net Rx counterparts.
  #endif
  
negative.code: 
    /// Returns a stream that produces elements from both of the given streams so
    /// that elements from the streams are interleaved non-deterministically in
    /// the returned stream.  See also: `mergeMap`, `nil`.
  #if DOC
    ///
    /// Reference implementation:
  