/**
* Creates string res of leftSon's toString, its own value and status, then rightSon's toString
*
* @return res returns the entire mathematical equation and their status in the correct order
*/
public String toString() {
String res = "";
if (this.leftSon != null) res += "{" + leftSon.toString() + "}";
res += "{" + cellValue + ",status=" + status + "}";
if (this.rightSon != null) res += "{" + rightSon.toString() + "}";
return res;
}
