protected static boolean isCommutative(int operator) {
        return (operator == Token.AND ||
                operator == Token.OR ||
                operator == Token.UNION ||
                operator == Token.INTERSECT ||
                operator == Token.PLUS ||
                operator == Token.MULT ||
                operator == Token.EQUALS ||
                operator == Token.FEQ ||
                operator == Token.NE ||
                operator == Token.FNE
                );
    }