public virtual void Remove(EulerTourNode root)
 {
     if (!_dict.Remove(root))
     {
         throw new ArgumentException();
     }
 }
 public void Remove(EulerTourNode root) => _count--;
 public virtual void Add(EulerTourNode root, ConnVertex vertex)
 {
     _dict.Add(root, vertex);
 }
 public void Add(EulerTourNode root, ConnVertex vertex) => _count++;