anchor.diff:      // note that (Reduce Start) is the "Accept" action.
       | Reduce of 'Nonterminal
   
  +    /// <inherit />
  +    override this.ToString () =
  +        match this with
  +        | Shift terminal ->
  +            "Shift " + terminal.ToString ()
  +        | Reduce nonterminal ->
  +            "Reduce " + nonterminal.ToString ()
  +
   /// A node in a Parser State Position Graph (PSPG).
   type internal ParserStatePositionGraphNode<'Nonterminal, 'Terminal, 'Lookahead
       when 'Nonterminal : comparison
  
positive.code:     | Item of LrItem<'Nonterminal, 'Terminal, 'Lookahead>
      /// A parser action.
      | Action of ParserStatePositionGraphAction<'Nonterminal, 'Terminal>
  
  /// <summary>A Parser State Position Graph (PSPG).</summary>
  /// <remarks>
  
negative.code:                     Set.add item nonfreeItems)
  
      //
      let ofGrammar (grammar : AugmentedGrammar<'Nonterminal, 'Terminal>, lr0ParserTable : Lr0ParserTable<'Nonterminal, 'Terminal>) =
          // Compute the parser state position graphs of the LR(0) parser states of the augmented grammar.
          let positionGraphs = positionGraphs grammar lr0ParserTable
  
  