Subject: File No. 4-657
From: Mathieu Rosenbaum, Ph.D
Affiliation: Professor of Probability and Finance, University Pierre and Marie Curie (Paris 6)

January 2, 2013

Dear Sir or Madam,

We think the attached paper, and particularly its Section 5, can be very relevant for your roundtable.

Indeed, in this work, we link microstructural properties of an asset to the tick value of the exchange.

As a consequence of that, we are able to predict the future microstructural features of an asset after a change in the tick value.

Therefore, we can determine beforehand what should the value of the tick be if the market designer has a certain set of high frequency statistics he wants to achieve.

Also we are able to define a notion of optimal tick value, which we believe is a crucial issue for market designers and regulators.

We hope this article can be helpful,

Yours sincerely,

Khalil Dayri and Mathieu Rosenbaum