ExcelFormulaParser.Engine.CalculationChain.DependencyGraph.AddDependency C# (CSharp) 메소드

        public virtual bool AddDependency(string from, string to)
        {
            if (_dict.Keys.Contains(from) && !_dict.Keys.Contains(to))
            {
                _items.Insert(_items.IndexOf(from), to);
                _dict[to] = true;
                return true;
            }
            else if (_dict.Keys.Contains(to) && !_dict.Keys.Contains(from))
            {
                _items.Insert(_items.IndexOf(to) + 1, from);
                _dict[from] = true;
                return true;
            }
            else if(_dict.Count == 0)
            {
                _items.Add(to);
                _items.Add(from);
                _dict[to] = true;
                _dict[from] = true;
                return true;
            }
            return false;
        }

 public virtual void Add(string from, string to)
 {
     var graph = GetGraph(from, to);
     if (graph != null)
     {
         graph.AddDependency(from, to);
         SetGraph(from, graph);
         SetGraph(to, graph);
         return;
     }
     var newGraph = new DependencyGraph();
     newGraph.AddDependency(from, to);
     _graphsDictionary.Add(from, newGraph);
     _graphsDictionary.Add(to, newGraph);
     _graphs.Add(newGraph);
 }