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                                                                    EXHIBIT 3.15

                              AMENDED AND RESTATED
                                     BYLAWS
                                       OF
                             HAAS INVESTMENT COMPANY

         The Bylaws of Haas Investment Company have been amended and restated in
their entirety by resolution of the Board of Directors of the corporation dated
June 27, 1991, as follows:

                                    ARTICLE I

                            MEETINGS OF STOCKHOLDERS

         1.       ANNUAL MEETING. The annual meeting of the stockholders for the
election of directors and the transaction of such other business as may come
before the meeting shall be held each year on the first Tuesday in May, at 10:00
o'clock A.M., unless a different hour is specified in the notice or waiver of
notice.

         2.       SPECIAL MEETINGS. A special meeting of the stockholders may be
called at any time by the President or Vice President or by the holders of a
majority of the shares of stock then issued and outstanding.

         3.       PLACE OF MEETINGS. All meetings shall be held at the
corporation's principal office in Lincoln, Nebraska, unless a different place is
specified in the notice or waiver of notice.

         4.       NOTICE OF MEETINGS. Written notice of the time and place shall
be mailed to each stockholder at least five days before such meeting. Written
notice of the time and place of a special meeting, and of the purpose for which
the meeting is called, shall be mailed to each stockholder at least five days
before any such meeting. No notice shall be required as to any stockholder who
signs a written waiver of notice of the meeting.


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         5.       QUORUM. The presence at any regular or special meeting, in
person or by proxy, of the holders of record of a majority of the shares of
stock then issued and outstanding shall constitute a quorum for the transaction
of business. If a quorum is not present, the stockholders who are present may
adjourn the meeting until a quorum is present. At any adjourned meeting at which
a quorum is present, any business may be transacted which could have been
transacted at the meeting as originally called.

         6.       VOTING. All matters shall be decided by a majority of the
shares present and voting at any meeting, unless otherwise provided by statute
or by the Articles of Incorporation. Corporate stockholders shall be represented
by either its President or Vice President.

                                   ARTICLE II

                               BOARD OF DIRECTORS

         1.       GENERAL POWERS. The business of the corporation shall be
managed by the Board of Directors and the officers, but all matters of policy
shall be determined by the Board of Directors.

         2.       NUMBER. There shall be at least 3 director(s).

         3.       ELECTION. The first Board of Directors shall be appointed by
the incorporator to serve until the first special or annual meeting of the
stockholders and until their successors are elected and qualified. Thereafter,
the stockholders shall elect directors to serve until the next annual meeting
and until their


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successors are elected and qualified. Directors need not be stockholders.

         4.       RESIGNATIONS AND VACANCIES. The stockholders or the Board of
Directors may accept the resignation of a director before the director's term
has expired. Vacancies in the Board of Directors shall be filled by the
stockholders in accordance with the provisions of Article II, Section 3, or by
the remaining directors.

                                   ARTICLE III

                              MEETING OF DIRECTORS

         1.       ANNUAL MEETING. The annual meeting of the Board of Directors
for the election of officers and transaction of such other business as may come
before the meeting shall be held immediately following the adjournment of the
annual meeting of stockholders and at the same location.

         2.       SPECIAL MEETINGS. Special meetings of the Board of Directors
may be held at any time and place on call of the President or Vice-President or
any director. Reasonable notice of the time and place thereof shall be given
orally or in writing to the director, unless such notice is waived by the
director in writing.

         3.       QUORUM. A majority of the directors shall constitute a quorum
at any meeting and any action by the Board of Directors shall require the
affirmative vote of a majority of those present. In the absence of a quorum, the
director or directors


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present may adjourn the meeting from time to time until a quorum is present.

                                   ARTICLE IV

                                    OFFICERS

         1.       OFFICERS. The corporation shall have a President, a Vice
President, a Secretary and a Treasurer, and the same person may hold two or more
of said offices, except that the President may not also hold the office of Vice
President.

         2.       ELECTION. Officers shall be elected annually and shall serve
until their successors are elected and qualified. Officers need not be directors
or stockholders.

         3.       REMOVAL. The Board of Directors may, at a meeting called for
that purpose remove any officer.

         4.       RESIGNATIONS AND VACANCIES. The Board of Directors may accept
the resignation of an officer. A vacancy in any office may be filled by the
Board of Directors.

                                    ARTICLE V

                         DUTIES AND SALARIES OF OFFICERS

         1.       PRESIDENT. The President shall be the chief executive officer
of the corporation. The President shall preside at all meetings of the
stockholders and the directors; shall see that all orders and resolutions of the
Board of Directors are carried into effect; and shall execute bonds, notes,
deeds, mortgages, contracts and other instruments for the corporation.

         2.       VICE PRESIDENT. In the absence of the President, or in the
event of his inability to act as such, the Vice President


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may perform the duties of the President. The Vice President shall assist the
President and shall perform such duties as are assigned by the Board of
Directors.

         3.       SECRETARY. The Secretary shall issue necessary notices of
meetings, shall keep the minutes, shall have charge of the seal, and shall sign
such instruments as require the Secretary's signature, and shall perform all
duties incident to the office or that are properly required by the Board of
Directors.

         4.       TREASURER. The Treasurer shall see that the books of account
are kept and are balanced each month, and that such financial statements or
reports are prepared as the Board of Directors may require.

         5.       SALARIES. The salaries of all officers and agents of the
corporation shall be fixed by the Board of Directors.

                                   ARTICLE VI

                                  CAPITAL STOCK

         1.       CERTIFICATES. Certificates of stock shall be issued to holders
of fully paid stock in numerical order from the stock certificate book, and
shall be signed by the President and by the Secretary and impressed with the
corporate seal. A record of each certificate issued shall be kept on a stub
thereof.

         2.       TRANSFER. Transfers of stock shall be made upon the books of
the company; and before a new certificate is issued, the old certificate must be
surrendered for cancellation.

         3.       RESTRICTED SALE AND ASSIGNMENT. The sale and transfer of stock
in the corporation by the original stockholders


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may be restricted, and by acceptance of the original stock certificates, each
stockholder may agree that the stockholder's stock cannot be sold or transferred
to any third party without first being offered for sale to the corporation at a
price to be agreed upon by separate written agreement, or if none, by the
corporation and stockholders annually. Each certificate of stock shall then
contain the following or substantially similar language: "Transfer of this
certificate and the stock represented thereby is restricted in accordance with
the records of the corporation."

                                   ARTICLE VII

                                    DIVIDENDS

         The Board of Directors may, subject to the laws and statutes of
Nebraska and the Articles of Incorporation, declare dividends on the capital
stock of the corporation. Dividends may be paid in cash, in property, or in
shares of the capital stock of the corporation at part.

                                  ARTICLE VIII

                                   AMENDMENTS

         These Bylaws may be amended or repealed at any meeting of the Board of
Directors.

                                   CERTIFICATE

         I hereby certify that the foregoing are the Bylaws duly approved and
adopted at the first meeting of the shareholders of the aforesaid corporation.

                                                DATED this 27 day of June, 1991.


                                                      /s/ Mildred Haas
                                             -----------------------------------
                                                          Secretary


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