Later, they can sell their copy back to Chegg if it's in "very good or better" condition.

MSN: Fast-Growing Chegg Aims for High Marks with Students

Once the protection expires, the first company to challenge the patent gets an exclusive right to sell the copy for 180 days.

BBC: Novartis: India rejects patent plea for cancer drug Glivec

That means that it will almost certainly get the exclusive right to sell a copy of Lipitor for six months, a period during which it will be able to price a generic at almost the full cost of Lipitor.

FORBES: Pfizer Wins Longer Life For Lipitor