Before revision:  In this paper we consider the problem of sorting unsigned permutations by prefix reversals and prefix transpositions , where a prefix reversal or a prefix transposition is applied always at the unsorted suffix of the given permutation.
After revision:  In this paper we considerpancake flipping problem the problem of sorting unsigned permutations by prefix reversals and prefix transpositions , where a prefix reversal or a prefix transposition is applied always at the unsorted suffix of the given permutation.