!! +exec+ +var+ +string+
$lst_tit listcomplement$lst_titend$type_both
  $(lst_syntax)listcomplement $emph list1$emphend in $emph list2$emphend</tt>
  $lst_mean 返回出现在 $emph list2$emphend 内但不出现在
  $emph list1$emphend 内的项. 重复出现被删除.

