public String toString0(){
		String operator = "";
		switch(this.op){
		case plus:
			operator = "+"; break;
		case minus:
			operator = "-"; break;
		case times:
			operator = "*"; break;
		case devide:
			operator = "/"; break;
		case biggerThan:
			operator = ">"; break;
		case lessThan:
			operator = "<"; break;
		case equal:
			operator = "="; break;
		case and:
			operator = "and"; break;
		case or:
			operator = "or"; break;
		}
		return e1.toString() + " " + operator + " " + e2.toString();
	}