[Haskell-beginners] A problem about Haskell 99 questions

In problem 7 http://www.haskell.org/haskellwiki/99_questions/1_to_10, the example in haskell is below: *Main> flatten (Elem 5)[5]*Main> flatten (List [Elem 1, List [Elem 2, List [Elem 3, Elem 4], Elem 5]])[1,2,3,4,5]*Main> flatten (List [])[]

What are the functions List and Elem? I cann't hoogle it.