
<PAGE>
                                                                  EXHIBIT (A)(6)

            GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION
                         NUMBER ON SUBSTITUTE FORM W-9

GUIDELINES FOR DETERMINING THE PROPER IDENTIFICATION NUMBER TO GIVE THE PAYER.--
Social Security numbers have nine digits separated by two hyphens: i.e.,
000-00-0000. Employer identification numbers have nine digits separated by only
one hyphen: i.e., 00-0000000. The table below will help determine the number to
give the payer.
<TABLE>
<CAPTION>
-----------------------------------------------------------

                                    GIVE THE NAME AND
                                    SOCIAL SECURITY
FOR THIS TYPE OF ACCOUNT:           NUMBER OF--
-----------------------------------------------------------
<S>        <C>                      <C>
1.         Individual               The individual

2.         Two or more individuals  The actual owner of the
           (joint account)          account or, if combined
                                    funds, the first
                                    individual on the
                                    account(1)

3.         Custodian account of a   The minor(2)
           minor (Uniform Gift to
           Minors Act)

4.         a. The usual revocable   The grantor-trustee(1)
           savings trust (grantor
           is also trustee)

           b. So-called trust       The actual owner(1)
           account that is not a
           legal or valid trust
           under state law

5.         Sole proprietorship      The owner(3)

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

<CAPTION>
                                    GIVE THE NAME AND
                                    EMPLOYER
                                    IDENTIFICATION
FOR THIS TYPE OF ACCOUNT:           NUMBER OF--
<S>        <C>                      <C>
-----------------------------------------------------------
6.         A valid trust, estate,   The legal entity(4)
           or pension trust

7.         Corporate                The corporation

8.         Association, club,       The organization
           religious, charitable,
           educational or other
           tax-exempt organization

9.         Partnership              The partnership

10.        A broker or registered   The broker or nominee
           nominee

11.        Account with the         The public entity
           Department of
           Agriculture in the name
           of a public entity
           (such as a state or
           local government,
           school district, or
           prison) that receives
           agricultural program
           payments
</TABLE>

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

(1) List first and circle the name of the person whose number you furnish. If
    only one person on a joint account has a social security number, that
    person's number must be furnished.

(2) Circle the minor's name and furnish the minor's social security number.

(3) You must show your individual name, but you may also enter your business or
    "doing business as" name. You may use either your social security number or
    employer identification number (if you have one).

(4) List first and circle the name of the legal trust, estate, or pension trust.
    (Do not furnish the identifying number of the personal representative or
    trustee unless the legal entity itself is not designated in the account
    title.)

NOTE:  If no name is circled when there is more than one name, the number will
       be considered to be that of the first name listed.
<PAGE>
OBTAINING A NUMBER

If you don't have a taxpayer identification number or you don't know your
number, obtain Form SS-5, Application for a Social Security Number, or Form
SS-4, Application for an Employer Identification Number, at the local office of
the Social Security Administration or the Internal Revenue Service and apply for
a number. United States resident aliens who cannot obtain a social security
number must apply for an ITIN (Individual Taxpayer Identification Number) on
Form W-7.

PAYEES EXEMPT FROM BACKUP WITHHOLDING

Payees specifically exempted from backup withholding on payments of interest,
dividends and with respect to broker transactions include the following:

    - A corporation.

    - A financial institution.

    - An organization exempt from tax under section 501(a), or an individual
      retirement plan.

    - The United States or any agency or instrumentality thereof.

    - A state, the District of Columbia, a possession of the United States, or
      any political subdivision or instrumentality thereof.

    - A foreign government, or any political subdivision, agency or
      instrumentality thereof.

    - An international organization or any agency or instrumentality thereof.

    - A dealer in securities or commodities required to register in the United
      States, the District of Columbia, or a possession of the United States.

    - A real estate investment trust.

    - A common trust fund operated by a bank under section 584(a).

    - An exempt charitable remainder trust, or a non-exempt trust described in
      section 4947.

    - An entity registered at all times under the Investment Company Act of
      1940.

    - A foreign central bank of issue.

Payments of dividends and patronage dividends not generally subject to backup
withholding include the following:

    - Payments to nonresident aliens subject to withholding under section 1441.

    - Payments to partnerships not engaged in a trade or business in the United
      States and which have at least one nonresident alien partner.

    - Payments of patronage dividends not paid in money.

    - Payments made by certain foreign organizations.

    - Payments made to a middleman known in the investment community as a
      nominee or who is listed in the most recent publication of the American
      Society of Corporate Secretaries, Inc., Nominee List.

Payments of interest not generally subject to backup withholding include the
following:

    - Payments of interest on obligations issued by individuals. Note: You may
      be subject to backup withholding if this interest is $600 or more and is
      paid in the course of the payer's trade or business and you have not
      provided your correct taxpayer identification number to the payer.

    - Payments of tax-exempt interest (including exempt-interest dividends under
      section 852).

    - Payments described in section 6049(b)(5) to nonresident aliens.

    - Payments on tax-free covenant bonds under section 1451.

    - Payments made by certain foreign organizations.

    - Payments made to a middleman known in the investment community as a
      nominee or who is listed in the most recent publication of the American
      Society of Corporate Secretaries, Inc., Nominee List.

Exempt payees described above should file Substitute Form W-9 to avoid possible
erroneous backup withholding.

FILE THIS FORM WITH THE PAYER, FURNISH YOUR TAXPAYER IDENTIFICATION NUMBER,
WRITE "EXEMPT" ON THE FACE OF THE FORM, AND RETURN IT TO THE PAYER. IF THE
PAYMENTS ARE INTEREST, DIVIDENDS, OR PATRONAGE DIVIDENDS, ALSO SIGN AND DATE THE
FORM.

PENALTIES

(1)  PENALTY FOR FAILURE TO FURNISH TAXPAYER IDENTIFICATION NUMBER.--If you fail
to furnish your taxpayer identification number to a payer, you are subject to a
penalty of $50 for each such failure unless your failure is due to reasonable
cause and not to willful neglect.

(2) CIVIL PENALTY FOR FALSE INFORMATION WITH RESPECT TO WITHHOLDING.--If you
make a false statement with no reasonable basis which results in no imposition
of backup withholding, you are subject to a penalty of $500.

(3)  CRIMINAL PENALTY FOR FALSIFYING INFORMATION.--Willfully falsifying
certifications or affirmations may subject you to criminal penalties including
fines and/or imprisonment.

FOR ADDITIONAL INFORMATION CONTACT YOUR TAX CONSULTANT OR THE INTERNAL REVENUE
SERVICE
