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                                                                    Exhibit 24.6

                                POWER OF ATTORNEY

STATE OF MICHIGAN
COUNTY OF WASHTENAW


         KNOW ALL MEN BY THESE PRESENTS that B. Joseph White, having an address
at The University of Michigan, 701 Tappan, has made, constituted and appointed
and BY THESE PRESENTS, does make, constitute and appoint Douglas Crocker II and
Michael J. McHugh, or either of them, having an address at Two North Riverside
Plaza, Chicago, Illinois 60606, his true and lawful Attorney-in-Fact for him and
his name, place and stead to sign and execute in any and all capacities this
Annual Report on Form 10-K and any or all amendments to this Annual Report
granting unto each of such, Attorney-in-Fact, full power and authority to do and
perform each and every act and thing, requisite and necessary to be done in and
about the premises, as fully, to all intents and purposes as he might or could
do if personally present at the doing thereof, with full power of substitution
and revocation, hereby ratifying and confirming all that each of such
Attorney-in-Fact or his substitutes shall lawfully do or cause to be done by
virtue hereof.

         This Power of Attorney shall remain in full force and effect until
terminated by the undersigned through the instrumentality of a signed writing.

         IN WITNESS WHEREOF, B. Joseph White, has hereunto set his hand this
20th day of February, 2002.


                                                  /s/ B. Joseph White
                                                  -----------------------------
                                                  B. Joseph White

         I, M. Catherine Rector, a Notary Public in and for said County in the
State of aforesaid, do hereby certify that B. Joseph White, personally known to
me to be the same person whose name is subscribed to the foregoing instrument
appeared before me this day in person and acknowledged that he signed and
delivered said instrument as his own free voluntary act for the uses and
purposes therein set forth.

         Given under my hand and notarial seal this 20th day of February, 2002.


                                                  /s/ M. Catherine Rector
                                                  -----------------------
                                                     (Notary Public)


                                           [SEAL]
My Commission Expires:___________________