!! +exec+ +var+ +string+
$lst_tit listunion$lst_titend$type_both
  $(lst_syntax)listunion $emph list1$emphend and $emph list2$emphend</tt>
  $lst_mean 返回出现在 $emph list1$emphend 或
  $emph list2$emphend 中之一的项. 重复的项被删除.

