A secret formula for eternal youth, f (x), was discovered by Dr. Quick, who has been working in our biotech company. However, Dr. Quick has disappeared and is rumored to be negotiating with a rival organization. From the notes that Dr. Quick left behind in his hasty exit it is clear that f (0) = 0, f (1) = 2, and that f [x0,x1,x2] = 1 for any three points x0,x1,x2. Find f (x).