private Operator parseOperator(String operator) {
		if (operator.equals("==")) return Operator.EQ;
		if (operator.equals(">")) return Operator.GT;
		if (operator.equals(">=")) return Operator.GTE;
		if (operator.equals("<")) return Operator.LT;
		if (operator.equals("<=")) return Operator.LTE;
		if (operator.equals("!=")) return Operator.NE;
		throw new IllegalArgumentException("unknown operator: " + operator);
	}