Document:

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                                                                   Exhibit 4.12a

                          TRANSFER OF THIS CERTIFICATE
                          IS SUBJECT TO THE CONDITIONS
                          SET FORTH IN THE DECLARATION
                                REFERRED TO BELOW

Number: 1                                             Common Securities: 241,238

                    Certificate Evidencing Common Securities

                                       of

                               PWG Capital Trust I

                          8.30% Common Trust Securities
                  (liquidation amount $25 per Common Security)

                  PWG Capital Trust I, a business trust formed under the laws of
the State of Delaware (the "Trust"), hereby certifies that Paine Webber Group
Inc. (the "Holder") is the registered owner of 241,238 common securities of the
Trust representing undivided beneficial interests in the assets of the Trust
designated the 8.30% Common Trust Securities (liquidation amount $25 per Common
Security) (the "Common Securities"). The transfer of Common Securities is
registrable on the books and records of the Trust, in person or by a duly
authorized attorney, upon surrender of this certificate duly endorsed and in
proper form for registration of transfer and satisfaction of the other
conditions set forth in the Declaration (as defined below) including, without
limitation, Section 9.01(c) thereof. The designations, rights, privileges,
restrictions, preferences and other terms and provisions of the Common
Securities are set forth in, and this certificate and the Common Securities
represented hereby are issued and shall in all respects be subject to the terms
and provisions of, the Amended and Restated Declaration of Trust of the Trust
dated as of December 9, 1996, as the same may be amended from time to time (the
"Declaration"), including the designation of the terms of Common Securities as
set forth in Exhibit C thereto. The Common Securities and the Preferred
Securities issued by the Trust pursuant to the Declaration represent undivided
beneficial interests in the assets of the Trust, including the Debentures (as
defined in the Declaration) issued by Paine Webber Group Inc., a Delaware
corporation, to the Trust pursuant to the Indenture referred to in the
Declaration. The Trust will furnish a copy of the Declaration and the Indenture
to the Holder without charge, upon written request to the Trust, at its
principal place of business or registered office.

                  The Holder of this Certificate, by accepting this Certificate,
is deemed to have agreed to the terms of the
<PAGE>   2
                                                                               2

Indenture and the Debentures, including that the Debentures are subordinate and
junior in right of payment to all Senior Indebtedness (as defined in the
Indenture) as and to the extent provided in the Indenture.
<PAGE>   3
                                                                               3

                  Upon receipt of this certificate, the Holder is bound by the
Declaration and is entitled to the benefits thereunder.

                  IN WITNESS WHEREOF, the Trustees of the Trust have executed
this certificate this 9th day of December, 1996.

                                         PWG Capital Trust I,

                                           by
                                              ----------------------------------
                                                  Name:
                                                  Title:  Regular Trustee

                                           by
                                              ----------------------------------
                                                  Name:
                                                  Title:  Regular Trustee

Dated:  December 9, 1996

Countersigned and Registered:

The Chase Manhattan Bank, as
Transfer Agent and Registrar

by
   --------------------------
       Authorized Officer
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                                                                               4

                                   ASSIGNMENT

FOR VALUE RECEIVED, the undersigned assigns and transfers this Common Security
Certificate to:

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

(Insert assignee's social security or tax identification
number)

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

(Insert address and zip code of assignee)

and irrevocably appoints

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

agent to transfer this Common Security Certificate on the books of the Trust.
The agent may substitute another to act for him or her.

Date:
       ------------------------

Signature:
            -------------------

(Sign exactly as your name appears on the other side of this Common Security
Certificate)<PAGE>   1
                                                                   Exhibit 4.12b

                          TRANSFER OF THIS CERTIFICATE
                          IS SUBJECT TO THE CONDITIONS
                          SET FORTH IN THE DECLARATION
                                REFERRED TO BELOW

Number: 2                                            Common Securities:  245,877

                    Certificate Evidencing Common Securities

                                       of

                              PWG Capital Trust II

                          8.08% Common Trust Securities
                  (liquidation amount $25 per Common Security)

         PWG Capital Trust II, a business trust formed under the laws of the
State of Delaware (the "Trust"), hereby certifies that Paine Webber Group Inc.
(the "Holder") is the registered owner of 245,877 common securities of the Trust
representing undivided beneficial interests in the assets of the Trust
designated the "8.08% Common Trust Securities" (liquidation amount $25 per
Common Security) (the "Common Securities"). The transfer of Common Securities is
registrable on the books and records of the Trust, in person or by a duly
authorized attorney, upon surrender of this certificate duly endorsed and in
proper form for registration of transfer and satisfaction of the other
conditions set forth in the Declaration (as defined below) including, without
limitation, Section 9.01(c) thereof. The designations, rights, privileges,
restrictions, preferences and other terms and provisions of the Common
Securities are set forth in, and this certificate and the Common Securities
represented hereby are issued and shall in all respects be subject to the terms
and provisions of, the Amended and Restated Declaration of Trust of the Trust
dated as of March 14, 1997, as the same may be amended from time to time (the
"Declaration"), including the designation of the terms of
<PAGE>   2
                                                                               2

Common Securities as set forth in Exhibit C thereto. The Common Securities and
the Preferred Securities issued by the Trust pursuant to the Declaration
represent undivided beneficial interests in the assets of the Trust, including
the Debentures (as defined in the Declaration) issued by Paine Webber Group
Inc., a Delaware corporation, to the Trust pursuant to the Indenture referred to
in the Declaration. The Trust will furnish a copy of the Declaration and the
Indenture to the Holder without charge upon written request to the Trust at its
principal place of business or registered office.

                  The Holder of this Certificate, by accepting this Certificate,
is deemed to have agreed to the terms of the Indenture and the Debentures,
including that the Debentures are subordinate and junior in right of payment to
all Senior Indebtedness (as defined in the Indenture) as and to the extent
provided in the Indenture.
<PAGE>   3
                                                                               3

                                   ASSIGNMENT

FOR VALUE RECEIVED, the undersigned assigns and transfers this Common Security
Certificate to:

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
(Insert assignee's social security or tax identification number)

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
(Insert address and zip code of assignee)

and irrevocably appoints

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
agent to transfer this Common Security Certificate on the books of the Trust.
The agent may substitute another to act for him or her.

Date:
      --------------------------------

Signature:
            --------------------------

(Sign exactly as your name appears on the other side of this Common Security
Certificate)<PAGE>   1
                                                                    Exhibit 4.13

                                    GUARANTEE

                  For value received, UBS AG, a Swiss banking corporation
("UBS"), hereby unconditionally and irrevocably guarantees, as a primary obligor
and not merely as a surety, the obligations of UBS Americas Inc., a Delaware
corporation and the successor by merger to Paine Webber Group Inc. (the
"Company"), under the Amended and Restated Declaration of Trust of PWG Capital
Trust I, dated and effective as of December 9, 1996 (the "Declaration of
Trust"), by the trustees named therein, the Company and the holders from time to
time of undivided beneficial interests in the assets of PWG Capital Trust I
issued pursuant to the PWG I Declaration of Trust ("Holders of Outstanding
Securities"), including any amount as may be owed from time to time by the
Company under the Declaration of Trust, when and as the same shall become due
and payable, whether at maturity, upon acceleration, redemption or otherwise in
accordance with the terms of the Declaration of Trust.

                  UBS hereby waives presentment, demand for payment, protest and
acceptance of this guarantee and all notices to any person (whether of
nonpayment, dishonor, protest, extension of credit to the debtor or of other
matters referred to in the Declaration of Trust, or otherwise) with respect to
the Declaration of Trust or any related agreement or instrument. If the Company
fails punctually to make any timely payment under the Declaration of Trust, UBS
hereby agrees to cause any such payment to be made punctually when and as the
same shall become due and payable, whether at the stated maturity or by
declaration of acceleration, or otherwise, and as if such payment were made by
the Company.

                  UBS hereby agrees that this guarantee is an absolute, present
and continuing guarantee of payment and not of collectability and that its
obligations hereunder shall be unconditional, irrespective of the validity,
legality or enforceability of the Declaration of Trust, the absence of any
action to enforce the same or to collect from the Company, and the recovery of
any judgment against the Company or any action to enforce the same or any other
circumstance that might otherwise result in a legal or equitable discharge or
defense of a guarantor.
<PAGE>   2
                  UBS shall be subrogated to all rights of the Holders of
Outstanding Securities against the Company in respect of any amounts paid by UBS
pursuant to the provisions of this guarantee; provided, however, that UBS shall
not be entitled to enforce or to receive any payments arising out of, or based
upon, such right of subrogation until the principal of and interest on all
outstanding Securities (as defined in the Declaration of Trust) shall have been
paid in full.

                  This guarantee shall bind UBS and its successors and assigns.
This guarantee constitutes a direct, unconditional and unsecured obligation of
UBS. The obligations of UBS hereunder will be subordinated in right of payment
to the prior payment in full of the deposit liabilities of UBS and all other
liabilities of UBS (including all deposit liabilities and other liabilities of
the head office and all offices of UBS wherever located), except (i) any
liabilities which by their terms rank pari passu with or are subordinated to the
obligations of UBS under this guarantee; (ii) any liabilities which by their
terms rank pari passu with or are subordinated to liabilities which by their
terms rank pari passu with or are subordinated to the obligations of UBS under
this guarantee; and (iii) any Existing Junior Subordinated Obligations. For the
avoidance of doubt, the obligations of UBS hereunder will be senior to any
Existing Junior Subordinated Obligations and any liabilities which by their
terms are subordinated to the obligations of UBS under this guarantee.

                  This guarantee shall be governed by the laws of the State of
New York, without regard to the principles of conflicts of laws thereof.
<PAGE>   3
                  IN WITNESS WHEREOF, UBS has caused this guarantee to be
executed by its duly authorized officers as of the day and year first above
written.

                                                     UBS AG

                                                     By: ____________________
                                                         Name:
                                                         Title:

                                                     By: ____________________
                                                         Name:
                                                         Title:

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