Finding "sub-palindromes" 2: subsequences. The same task as Finding "sub-palindromes" but instead of finding substrings you must find subsequences that are not substrings.

eg1:

input: "12131331"
output: 
"11", "33", "111", "121", "131", "313", "333", "1111", "1331", "11311", "13331"
or 
"11", "33", "111", "333", "1111", "11311", "13331"


eg2:

input: "3333"
output: 
"33", "333"
or
(null)



Input is a string of printable ascii characters.
Output is a list of unique strings.
If a subsequence also appears as a substring it may be omitted.
Shortest code wins.
Haskell (119)
import Data.List
main=interact f
f a=show.nub.filter(\x-&gt;(not$isInfixOf a x)&amp;&amp;x==reverse x&amp;&amp;length x&gt;1)$subsequences a

Isn't too difficult with a builtin subsequences and nub... :)