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EXHIBIT 10.5

FOURTH AMENDMENT TO

TAX SHARING AGREEMENT

by and among

AT&T CORP.,

LIBERTY MEDIA CORPORATION,
for itself and each member of the Liberty Group,

TELE-COMMUNICATIONS, INC.,

LIBERTY VENTURES GROUP LLC,

LIBERTY MEDIA GROUP LLC,

TCI STARZ, INC.,

TCI CT HOLDINGS, INC.,

and

each Covered Entity listed on the signature pages hereof,

dated as of October 28, 1999

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        This Fourth Amendment, dated as of October 28, 1999 (this "Fourth
Amendment"), to the Tax Sharing Agreement (the "Agreement") dated as of March 9,
1999, as amended by the First Amendment (the "First Amendment") to the Tax
Sharing Agreement dated as of May 28, 1999, the Second Amendment (the "Second
Amendment") to the Tax Sharing Agreement dated as of September 24, 1999 and the
Third Amendment (the "Third Amendment") to the Tax Sharing Agreement dated as of
October 20, 1999, is entered into by and among AT&T Corp., a New York
corporation, Liberty Media Corporation, a Delaware corporation, for itself and
on behalf of each member of the Liberty Group, Tele-Communications, Inc., a
Delaware corporation, Liberty Ventures Group LLC, a Delaware limited liability
company, Liberty Media Group LLC, a Delaware limited liability company, TCI
Starz, Inc., a Colorado corporation, TCI CT Holdings, Inc., a Delaware
corporation, each Covered Entity listed on the signature pages hereof, and each
entity which becomes a party to the Agreement pursuant to Section 23 thereto.
Unless otherwise stated herein, capitalized terms used in this Fourth Amendment
shall have the meaning ascribed to such terms in the Agreement.

        WHEREAS, the parties have entered into the Agreement which governs the
sharing, allocation and reimbursement of federal, state, local and foreign taxes
by the members of the Common Stock Group and the Liberty Group; and

        WHEREAS, the parties now wish to amend the Agreement in certain respects
to clarify the intent of the parties with respect to the sharing, allocation and
reimbursement of federal, state, local and foreign taxes by the members of the
Common Stock Group and the Liberty Group and to make such other amendments, as
provided herein;

        NOW, THEREFORE, in consideration of the mutual covenants contained
herein, the parties hereby agree as follows:

        1.     "AGI Merger Agreement" shall mean the Amended and Restated
Agreement and Plan of Merger dated as of October 28, 1999.

        2.     The first sentence of Section 3(d)(i) shall be amended as
follows:

a.the words "Cayman LLC (as defined in the AGI Merger Agreement)," shall be
deleted;

b.the words "the Original Agreement (as defined in the AGI Merger Agreement),"
shall be inserted after the words "; the AGI Acquisition, the AGI Merger
Agreement," and before the words "the AGI Merger";

c.the words ", as amended" shall be inserted after the words "the First
Supplement to Inter-Group Agreement dated May 28, 1999" and before the words
"(the "First Supplement")";

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d.the words "the Fourth Amendment" shall be inserted after the words "this
Clause D of this First Amendment," and before the words "or the Voting Agreement
dated May 28, 1999"; and

e.the words ", the Fourth Amendment" shall be inserted after the words "this
Clause D of this First Amendment" and before the words "and the Voting Agreement
or executed".

        3.     Except as otherwise expressly provided herein, the Agreement
shall continue in full force and effect without modification.

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        IN WITNESS WHEREOF, each of the parties has caused this Fourth Amendment
to be executed by its respective duly authorized officer as of the date first
set forth above.

    AT&T CORP.
 
 
By:
 
/s/ Daniel E. Somers

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    Name:   Daniel E. Somers     Title:   Senior Executive Vice President
and Chief Financial Officer
 
 
LIBERTY MEDIA CORPORATION, for itself and for
each member of the Liberty Group
 
 
By:
 
/s/ Gary S. Howard

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    Name:   Gary S. Howard     Title:   Executive Vice President and Chief
Operating Officer

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Each of the Covered Entities listed below on this page hereby executes this
Fourth Amendment as a member of the Liberty Group to acknowledge that such
Person is bound by this Fourth Amendment as a member of the Liberty Group:

    LIBERTY SP, INC.
 
 
By:
 
/s/ Gary S. Howard

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    Name:   Gary S. Howard     Title:   Executive Vice President and Chief
Operating Officer
 
 
LIBERTY AGI, INC.
 
 
By:
 
/s/ Gary S. Howard

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    Name:   Gary S. Howard     Title:   Executive Vice President and Chief
Operating Officer
 
 
LMC INTERACTIVE, INC.
 
 
By:
 
/s/ Gary S. Howard

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    Name:   Gary S. Howard     Title:   Executive Vice President and Chief
Operating Officer

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    TELE-COMMUNICATIONS, INC.
 
 
By:
 
/s/ Steven M. Brett

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    Name:   Steven M. Brett     Title:   Sr. Executive Vice President
 
 
LIBERTY VENTURES GROUP LLC
 
 
By:
 
/s/ Steven M. Brett

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    Name:   Steven M. Brett     Title:   Vice President
 
 
LIBERTY MEDIA GROUP LLC
 
 
By:
 
/s/ Gary S. Howard

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    Name:   Gary S. Howard     Title:   Vice President
 
 
TCI STARZ, INC.
 
 
By:
 
/s/ Stephen M. Brett

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    Name:   Stephen M. Brett     Title:   Vice President
 
 
TCI CT HOLDINGS, INC.
 
 
By:
 
/s/ Stephen M. Brett

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    Name:   Stephen M. Brett     Title:   Vice President

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EXHIBIT 10.5