A farmer has a wolf, a chicken, and some corn. He wants to cross a river, but his boat can only hold himself and one other animal/item. If he leaves the wolf alone with the chicken, the wolf will eat the chicken; if he leaves the chicken alone with the corn, the chicken will eat the corn; if he leaves the wolf alone with the corn, the wolf will not eat the corn. Prove that the fewest number of trips to get all animals across is 7 (counting each direction separately)