[Haskell-beginners] Type question

Hi, I was playing around after getting the new O'Reilly book with lists and their operators! Not sure what the below actually means? Prelude> [] : [] [[]] it :: [[a]] (Got :set +t on ) I thought the first argument of ':' must be an element, so is the empty list an element of the same type of the contents of the empty list? Yours confused Paul :-)