public ArithmeticBinOpExpression(Expression left, Expression right, ArithmeticBinOp op)
 {
     _op = op;
     _children.Add(left);
     _children.Add(right);
 }
 public ArithmeticBinOpExpression(Expression left, Expression right, ArithmeticBinOp op)
 {
     _op = op;
     _children.Add(left);
     _children.Add(right);
 }