ΐΦΜμΜΓappΟΒΤΨ

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                                                                       EXHIBIT 6

                                                                January 10, 2000

GAP Coinvestment Partners, L.P.
c/o General Atlantic Service Corporation
β–� β–‡β–‡β–‡β–‡β–‡β–‡β–‡β–‡ β–‡β–‡β–‡β–‡β–�

Greenwich, CT  06380

Ladies and Gentlemen:

             You agreed in Section 3 of the Underwriting Agreement dated August
11, 1999 (the "Underwriting Agreement") among β–‡β–‡β–‡β–‡β–‡β–‡β–‡β–‡β–�.β–‡β–‡β–� Incorporated, the
selling shareholders and the underwriters to restrict your right to sell,
dispose and engage in certain other transactions in the common stock and common
stock equivalents of β–‡β–‡β–‡β–‡β–‡β–‡β–‡β–‡β–�.β–‡β–‡β–� for a 180 day period. We are writing to
release you from the restrictions set forth in the Underwriting Agreement with
respect to the sale of 1,000,000 shares of common shares of β–‡β–‡β–‡β–‡β–‡β–‡β–‡β–‡β–�.β–‡β–‡β–�.

             This release is subject to your agreement that the restrictions on
your right to sell, dispose or engage in certain other transactions in the
common stock and common stock equivalents of β–‡β–‡β–‡β–‡β–‡β–‡β–‡β–‡β–�.β–‡β–‡β–� in the Underwriting
Agreement shall be extended through the period ending on May 8, 2000, except
that you may sell, distribute, transfer or dispose of up to 15% of the common
stock of β–‡β–‡β–‡β–‡β–‡β–‡β–‡β–‡β–�.β–‡β–‡β–� you own after giving effect to the sale permitted by this
letter beginning on February 8, 2000.

             We have been advised by β–‡β–‡β–‡β–‡β–‡β–‡β–‡β–‡β–�.β–‡β–‡β–� that you will own 4,626,786
shares of common stock of β–‡β–‡β–‡β–‡β–‡β–‡β–‡β–‡β–�.β–‡β–‡β–� after giving effect to the sale
permitted by this letter. Please sign below to acknowledge your acceptance of
the terms of the release and the extension of the restrictions.


                                         Very truly yours,


                                         By: /s/ β–‡β–‡β–‡β–‡β–‡β–‡β–� β–�. β–‡β–‡β–‡β–‡β–‡β–‡β–�
                                             ----------------------
                                             β–‡β–‡β–‡β–‡β–‡β–‡β–� β–�. β–‡β–‡β–‡β–‡β–‡β–‡β–�
                                             Managing Director

Accepted by:
GAP Coinvestment Partners, L.P.


By: /s/ β–‡β–‡β–‡β–‡β–‡β–‡β–� β–�. β–‡β–‡β–‡β–‡
    -------------------
    β–‡β–‡β–‡β–‡β–‡β–‡β–� β–�. β–‡β–‡β–‡β–‡
    General Partner