Manipulation can occur in a variety of ways,from actions taken by insidersthat influence the stock price(e.g.,accounting and earnings manipulation suchas in the Enron case)to the release of false information or rumors in Internetchat rooms.Moreover,it is well known that large block trades can influenceprices.For example,by purchasing a large amount of stock,a trader can drivethe price up.If the trader can then sell shares and if the price does not adjustto the sales,then the trader can profit.Of course,we should expect that sucha strategy would not work.Selling shares will depress the stock price,so that,on average,the trader buys at higher prices and sells at lower prices.This isthe unraveling problem and would seem to rule out the possibility of trade-based manipulation.