( perm
  =   prefix List result original A Z
    .   !arg:(?.)
      |   !arg:(?prefix.?List:?original)
        & :?result
        &   whl
          ' ( !List:%?A ?Z
            & !result perm$(!prefix !A.!Z):?result
            & !Z !A:~!original:?List
            )
        & !result
  )
& out$(perm$(.a 2 "]" u+z);