EXHIBIT 4.1

CUSIP No. 003687209

AGREEMENT CONCERNING JOINT FILING OF SCHEDULE 13D

The undersigned agree as follows:

(i) each of them is individually eligible to use Schedule 13D to which this Exhibit is attached, and such Schedule 13D is filed on behalf of each of them; and

(ii) each of them is responsible for the timely filing of such Schedule 13D and any amendments thereto, and for the completeness and accuracy of the information concerning such person contained therein; but none of them is responsible for the completeness or accuracy of the information concerning the other person making the filing, unless such person knows or has reason to believe that such information is inaccurate.

This Agreement may be executed in any number of counterparts, each of which shall be deemed to be an original, but all of which, taken together, shall constitute one and the same instrument.

Dated as of December 6, 2011

1

V. PREM WATSA
/s/ V. Prem Watsa
1109519 ONTARIO LIMITED
By:	/s/ V. Prem Watsa
	Name:	V. Prem Watsa
	Title:	President
THE SIXTY TWO INVESTMENT COMPANY LIMITED
By:	/s/ V. Prem Watsa
	Name:	V. Prem Watsa
	Title:	President
810679 ONTARIO LIMITED
By:	/s/ V. Prem Watsa
	Name:	V. Prem Watsa
	Title:	President
FAIRFAX FINANCIAL HOLDINGS LIMITED
By:	/s/ V. Prem Watsa
	Name:	V. Prem Watsa
	Title:	Chairman and Chief Executive Officer

2

TIG INSURANCE COMPANY
By:	/s/ John. J. Bator
	Name:	John J. Bator
	Title:	Chief Financial Officer and Senior Vice President
FAIRMONT SPECIALTY INSURANCE COMPANY
By:	/s/ John. J. Bator
	Name:	John J. Bator
	Title:	Chief Financial Officer and Senior Vice President
GENERAL FIDELITY INSURANCE COMPANY
By:	/s/ John. J. Bator
	Name:	John J. Bator
	Title:	Chief Financial Officer and Senior Vice President

3

THE NORTH RIVER INSURANCE COMPANY
By:	/s/ Paul Bassaline
	Name:	Paul Bassaline
	Title:	Vice President & Controller
UNITED STATES FIRE INSURANCE COMPANY
By:	/s/ Paul Bassaline
	Name:	Paul Bassaline
	Title:	Vice President & Controller

4

ODYSSEY REINSURANCE COMPANY
By:	/s/ Kirk M. Reische
	Name:	Kirk M. Reische
	Title:	Vice President
CLEARWATER INSURANCE COMPANY
By:	/s/ Kirk M. Reische
	Name:	Kirk M. Reische
	Title:	Vice President

5

MARKEL INSURANCE COMPANY OF CANADA
By:	/s/ Craig Pinnock
	Name:	Craig Pinnock
	Title:	Director
COMMONWEALTH INSURANCE COMPANY
By:	/s/ Craig Pinnock
	Name:	Craig Pinnock
	Title:	Director
FEDERATED INSURANCE COMPANY OF CANADA
By:	/s/ Craig Pinnock
	Name:	Craig Pinnock
	Title:	Director
LOMBARD GENERAL INSURANCE COMPANY OF CANADA
By:	/s/ Craig Pinnock
	Name:	Craig Pinnock
	Title:	Director
LOMBARD INSURANCE COMPANY
By:	/s/ Craig Pinnock
	Name:	Craig Pinnock
	Title:	Director

6

ZENITH INSURANCE COMPANY
By:	/s/ Michael Jansen
	Name:	Michael Jansen
	Title:	Executive Vice President and General Counsel

7

SENECA INSURANCE COMPANY, INC.
By:	/s/ James V. Kraus
	Name:	James V. Kraus
	Title:	Assistant Vice President

8

FAIRFAX (BARBADOS) INTERNATIONAL CORP.
By:	/s/ Janice Burke
	Name:	Janice Burke
	Title:	Vice President and General Manager
WENTWORTH INSURANCE COMPANY LTD.
By:	/s/ Janice Burke
	Name:	Janice Burke
	Title:	Vice President and General Manager

9