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                                                                   EXHIBIT 10.17

                       ASSIGNMENT AND ASSUMPTION OF LEASE

         THIS ASSIGNMENT AND ASSUMPTION OF LEASE (this "Assignment") is made as
of _______________________, 2000 (the "Effective Date"), by and between
_______________________, a _________________________ ("Assignor"), and,
a ____________________________ ("Assignee").

A.       Assignor is the tenant under that certain lease set forth on Schedule 1
         attached hereto (the "Lease").

B.       Assignee is an affiliate of Assignor.

C.       Assignor has agreed to assign to Assignee all of Assignor's right,
         title, and interest in, to and under the Lease, and Assignee has agreed
         to assume all of the Assignor's duties and obligations under the Lease
         in accordance with the terms set forth herein.

                                   AGREEMENTS:

         NOW, THEREFORE, in consideration of the foregoing premises and the
respective agreements, covenants and conditions herein contained, and other good
and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged and agreed, as of the Effective Date Assignor and Assignee agree as
follows:

         1. Assignment. Assignor does hereby assign, transfer, convey and
deliver to Assignee, all of Assignor's right, title and interest, in, to and
under the Lease.

         2. Assumption. Assignee hereby accepts the foregoing assignment and
assumes and agrees to perform and discharge, as and when due, all of the
agreements, duties and obligations of Assignor under or in respect of the Lease
from and after the Effective Date, and Assignee agrees to be bound by all of the
terms and conditions of the Lease. Assignee shall succeed to the rights and
interests of Assignor under the Lease.

         3. Indemnity. Assignee agrees to indemnify Assignor and save Assignor
harmless from any and all liability, loss, damage, costs and expenses (including
reasonable attorneys' fees) that may arise from events occurring after the
Effective Date with respect to the Lease. Assignor agrees to indemnify Assignee
and save Assignee harmless from any and all liability, loss, damage, costs and
expenses (including reasonable attorneys' fees) that may arise from events
occurring through the Effective Date with respect to the Lease.

         4. Acceptance of Property. Assignee has inspected the property covered
by the Lease (the "Property") and accepts the Property "as is, where is" and
"with all faults". Assignor makes no representation or warranty, express or
implied, including without limitation any implied warranty of merchantability,
fitness for a particular purpose, or suitability for any intended commercial
use, with respect to such Property, and Assignee irrevocably waives and releases
Assignor from any such warranties. Without limiting the generality of Paragraph
2 above, Assignee hereby expressly assumes any and all obligations of the tenant
under the Lease to restore the Property or any part thereof at the expiration or
termination of the Lease.

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         5. Limitation of Liability. Except for claims made by third parties
that are covered by the indemnification obligations under this Assignment,
neither party to this Assignment shall be liable to the other for any special,
punitive, indirect, consequential or incidental damages, including without
limitation damages for loss of use, revenues, goodwill or profits, whether
arising out of any alleged negligence, breach of warranty or contract, strict
liability or otherwise, and Assignor and Assignee each hereby irrevocably waive,
discharge and release the other from any and all such damages.

         6. Consent by Landlord. The effectiveness of this Assignment is
conditioned upon the approval or consent of Landlord, to the extent and in the
form that such approval or consent is required under the Lease, which approval
Assignor shall use its reasonable efforts to obtain. Assignee agrees to execute
such documents and to take such actions as Assignor may reasonably request in
connection with obtaining the Landlord's consent or approval to this Assignment.
If any consent required by Landlord under the Lease is not received prior to the
Effective Date, the Effective Date of this Assignment shall be the date on which
such consent is received.

         7. Successors and Assigns. The provisions of this Assignment shall be
binding upon, and shall inure to the benefit of, the successors and assigns of
the Assignor and the Assignee, respectively.

         8. Cooperation. Assignor and Assignee each agree that at any time and
from time to time, upon the request of the other, Assignor and Assignee each
will execute and deliver any and all such further instruments and documents and
take such further action as the other may reasonably request in order to obtain
the benefits of this Assignment and of the rights and powers herein granted.

         9. Counterparts; Facsimile Signature. This Assignment may be executed
in any number of counterparts, and all of said counterparts when taken together
shall constitute one and the same instrument. This Assignment may be delivered
via facsimile, and a signed Assignment delivered via facsimile shall be deemed
an original for all purposes.

         IN WITNESS WHEREOF, Assignor and Assignee have caused their duly
authorized representatives to execute this Assignment as of the date first
written above.

ASSIGNOR:                            ASSIGNEE:

By:                                  By:
      -----------------------------         -----------------------------

Name:                                Name:
      -----------------------------         -----------------------------

Its:                                 Its:
      -----------------------------         -----------------------------

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                                 ACKNOWLEDGMENTS

COMMONWEALTH OF MASSACHUSETTS       )
                                    ) ss.
COUNTY OF                           ) ______________, 2000

         On this day, before me, personally appeared _________, who being by me
duly sworn, did say that he is the __________ of ____________, a
________________, and acknowledged said instrument to be his free act and deed
and the free act and deed of said _______.

                                 -------------------------------
                                 Notary Public
                                 My Commission Expires:

COMMONWEALTH OF MASSACHUSETTS       )
                                    ) ss.
COUNTY OF                           ) ______________, 2000

         On this day, before me, personally appeared _________, who being by me
duly sworn, did say that he is the __________ of ____________, a
________________, and acknowledged said instrument to be his free act and deed
and the free act and deed of said _______.

                                 -------------------------------
                                 Notary Public
                                 My Commission Expires:

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                                   SCHEDULE 1

                                      LEASE

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                                                                   EXHIBIT 10.18

                          [GTE CORPORATION LETTERHEAD]

[Date]

[Genuity Inc. Address]

Re:      Financial Support Agreement Regarding Guaranty of Obligation for the
         benefit of [___________________], dated__________

Ladies and Gentlemen:

In consideration of the agreement by GTE Corporation ("GTE") to issue or
continue to maintain the guaranty described above which is attached as Exhibit A
hereto (the "Guaranty") following the transfer of GTE's controlling interest in
Genuity Inc. ("Genuity") as contemplated by GTE and Bell Atlantic Corporation's
Supplemental Filing with the FCC on January 27, 2000 (the "Separation"), Genuity
agrees to pay GTE a fee pursuant to the following terms and conditions:

Guaranty Fee:                       Guaranty Fee shall be ____% per annum,
                                    calculated monthly, charged on the month-end
                                    outstanding balance of the Guaranty, as
                                    evidenced by the amortization schedule
                                    attached thereto or included therein, and
                                    will be payable semi-annually on June 30 and
                                    December 31 of each calendar year. If the
                                    Guaranty is outstanding for less than a full
                                    calendar month, Guaranty Fee shall be
                                    computed based on the outstanding balance of
                                    the Guaranty on each calendar day of such
                                    month that the Guaranty shall remain in
                                    effect.

Adjustment to Guaranty Fee:         The Guaranty Fee set forth above was
                                    determined based on the assumption that
                                    Genuity's credit rating post-Separation
                                    would be equivalent to the average of the
                                    ratings of BBB/Baa2 and BBB-/Baa3. GTE shall
                                    have a one-time right to increase, effective
                                    prospectively, the Guaranty Fee (the
                                    "Adjusted Guaranty Fee") if either one of
                                    the following events occurs: (i) Standard &
                                    Poor's issues a credit rating for Genuity of
                                    BB+ or less or (ii) Moody's issues a credit
                                    rating for Genuity of Ba1 or less. Such
                                    right may be exercised at any time by
                                    written notice to Genuity.

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                                    If either of the events described in (i) or
                                    (ii) above occurs, the Adjusted Guaranty Fee
                                    shall be determined by GTE by averaging the
                                    rates quoted to GTE by three nationally
                                    recognized banking institutions for a credit
                                    equivalent to the published credit ratings
                                    of Genuity. The Adjusted Guaranty Fee shall
                                    become the Guaranty Fee payable under this
                                    letter from and after the date on which GTE
                                    provides Genuity written notice of the
                                    Adjusted Guaranty Fee.

Payment of Fee:                     Guaranty Fee is due not later than 5
                                    business days following the end of each
                                    semi-annual payment period and shall be
                                    delivered by electronic funds transfer to
                                    [wire transfer instructions] or such other
                                    bank account as shall be provided to Genuity
                                    by GTE in writing at least 5 business days
                                    prior to the date of electronic funds
                                    transfer.

                                    In the event the Guaranty is terminated,
                                    replaced by Genuity or expires prior to the
                                    end of the semi-annual payment period,
                                    Guaranty Fee will be due not later than 5
                                    business days following the termination of
                                    all obligations of GTE under the Guaranty.

Late Payment Fee:                   A Late Payment Fee in the amount of prime
                                    rate plus 1.00% per annum, calculated daily,
                                    commencing on the day immediately following
                                    the due date and based upon the number of
                                    days elapsed prior to payment of all amounts
                                    due shall be included with any overdue
                                    payment of Guaranty Fee.

Duty of Inquiry:                    GTE shall have no obligation to consult with
                                    Genuity or make any independent
                                    investigation prior to any decision to honor
                                    or dishonor any payment request under the
                                    Guaranty.

Immediate Repayment:                If GTE makes any payment under the Guaranty,
                                    GTE agrees to notify Genuity in writing, at
                                    the address set forth at the end of this
                                    letter or such other address as shall be
                                    subsequently provided to GTE by Genuity in
                                    writing, within three business days of the
                                    amount of such payment, and Genuity agrees
                                    to pay such amount to GTE within one
                                    business day following the date of such
                                    written notice. A Late Payment Fee shall be
                                    applied to any amounts not received when
                                    due.

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Return of Documents:                Genuity shall present the Guaranty to GTE
                                    for cancellation at the address of GTE set
                                    forth at the end hereof, or such other
                                    address as shall be provided to Genuity by
                                    GTE in writing, following the termination of
                                    all obligations of GTE under the Guaranty.

Indemnification:                    Genuity will reimburse, indemnify and hold
                                    harmless GTE from and against any and all
                                    payments, losses, damages, costs and
                                    expenses (including attorneys' fees and
                                    court costs) paid or incurred by GTE, its
                                    officers, directors, agents, and employees,
                                    as a result of any claim made under this
                                    letter or the Guaranty.

Notice:                             Any written notice or other information
                                    required to be provided in writing hereunder
                                    shall be made in writing by overnight
                                    delivery service, facsimile transmission or
                                    electronic mail, that provides for evidence
                                    of receipt.

Waiver:                             No waiver hereunder shall be effective
                                    unless evidenced in writing, and shall be
                                    effective only under the circumstances
                                    specifically described in such waiver.

Underlying Documents:               Genuity agrees to provide GTE with an
                                    executed copy of each document entered into
                                    by Genuity as of the date first above
                                    written and from time to time which creates
                                    an obligation of Genuity that is guaranteed
                                    by the Guaranty, at the address of GTE set
                                    forth at the end hereof, or such other
                                    address as shall be provided to Genuity by
                                    GTE in writing.

Underlying Obligation:              Nothing herein shall modify any term of the
                                    Guaranty unless specifically provided
                                    herein.

Governing Law:                      New York.

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Please evidence your acceptance of the terms of this letter by executing below,
and return a duplicate original of this letter, together with copies of all
underlying documents which create an obligation of Genuity that is guaranteed by
the Guaranty, to GTE at the address set forth below.

GTE Corporation

By:  ____________________________

Title:____________________________

Notices to be delivered to:         ___________________________

                                    ___________________________

                                    ___________________________

Accepted this ____ day of _________, 2000

Genuity Inc.

By: _____________________________

Title:____________________________

Notices to be delivered to:         ___________________________

                                    ___________________________

                                    ___________________________

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