/// <summary>
 /// Get all references that aren't part of another reference expression
 /// </summary>
 public IEnumerable <ParseTreeNode> References()
 {
     return(ExcelFormulaParser
            .AllNodes(AllNodes, GrammarNames.Formula)
            .Where(node => node.ChildNodes.Count == 1 && node.ChildNodes[0].Is(GrammarNames.Reference))
            .Select(node => node.ChildNodes[0]));
 }
 /// <summary>
 /// Provide formula analysis functions
 /// </summary>
 public FormulaAnalyzer(string formula) : this(ExcelFormulaParser.Parse(formula))
 {
 }