EXHIBIT A


                 RELEVANT SUBSIDIARIES OF PARENT HOLDING COMPANY

PART A: TCW ENTITIES

PARENT HOLDING COMPANY:

      The TCW Group, Inc.



RELEVANT SUBSIDIARIES THAT ARE PERSONS DESCRIBED IN RULE 13d-1(b):

(i)   TCW Asset Management Company, a California corporation and an Investment
      Adviser registered under Section 203 of the Investment Advisers Act of
      1940.

This Schedule 13G is being filed by the TCW Group, Inc., a Nevada corporation
("TCW"), on behalf of itself and its direct and indirect subsidiaries, which
collectively constitute The TCW Group, Inc. business unit (the "TCW Business
Unit" or the "Reporting Person"). The TCW Business Unit is primarily engaged in
the provision of investment management services.

As of July 6, 2001, the ultimate parent company of TCW is Societe Generale,
S.A., a corporation formed under the laws of France ("SG"). The principal
business of SG is acting as a holding company for a global financial services
group, which includes certain distinct specialized business units that are
independently operated, including the TCW Business Unit.

SG, for purpose of the federal securities laws, may be deemed ultimately to
control TCW and the TCW Business Unit. SG, its executive officers and directors,
and its direct and indirect subsidiaries (including all business units except
the TCW Business Unit), may beneficially own shares of the securities of the
issuer to which this schedule relates (the "Shares") and such shares are not
reported in this statement. In accordance with Securities and Exchange
Commission ("SEC") Release No. 34-39538 (January 12, 1998), and due to the
separate management and independent operation of its business units, SG
disclaims beneficial ownership of Shares beneficially owned by the Reporting
Person. The Reporting Person disclaims beneficial ownership of Shares
beneficially owned by SG and any of SG's other business units.

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