mr. liebowitz said but i think he said it well.every conception should be challenged regularly with market's changing as fast as they are. that demands some flexibility from the standpoint of the clearing changes. there are capabilities to ensure batboy there remains liquidity. from the standpoint of being able to respond to attack, we think this is a corporate issue for congress to focus on. >> take as much time as you want. >> thank you. mr. knowlem, i will ask you this question. i would like the others to respond as well. as i said in my statement, i am concerned about the way some traders were canceled. given that everyone seems to agree the system work the way it was set up to do, how do you justify cancelling trade and protecting investors from the bad decisions? >> a share much of your concern. it was a difficult day to make that decision. it was done in coordination with the other markets on an ongoing discussion. that lasted many hours trying to decide what the proper decision would base. we were trying to balance the need