public ExpressionOperation(Operation operation, ExpressionNode left, ExpressionNode right)
     : base(left, right)
 {
     _operation = operation;
 }
 public ExpressionNode(ExpressionNode _l = null, ExpressionNode _r = null)
 {
     _leftNode = _l;
     _rightNode = _r;
 }
 public ExpressionOperation(Operation operation, ExpressionNode left, ExpressionNode right)
     : base(left, right)
 {
     _operation = operation;
 }