有三个关系 R、S 和 T 如下： <table border="1" cellspacing="0" cellpadding="0" _dj="MsoNormalTable"><tbody><tr><td width="38">R</td><td width="38"> </td><td width="57"> </td><td width="38">S</td><td width="38"> </td><td width="57"> </td><td width="38">T</td><td width="38"> </td><td width="38"> </td></tr><tr><td width="38">A</td><td width="38">B</td><td width="57"> </td><td width="38">B</td><td width="38">C</td><td width="57"> </td><td width="38">A</td><td width="38">B</td><td width="38">C</td></tr><tr><td width="38">m</td><td width="38">1</td><td width="57"> </td><td width="38">1</td><td width="38">3</td><td width="57"> </td><td width="38">m</td><td width="38">1</td><td width="38">3</td></tr><tr><td width="38">n</td><td width="38">2</td><td width="57"> </td><td width="38">3</td><td width="38">5</td><td width="57"> </td><td width="38"> </td><td width="38"> </td><td width="38"> </td></tr></tbody></table>由关系 R 和 S 通过运算得到关系 T，则所使用的运算为（）。