Joint Filing Agreement ----------------------

                             Joint Filing Agreement
                             ----------------------


         Each of the undersigned hereby acknowledges and agrees, in compliance
with the provisions of Rule 13d-1(k)(1) promulgated under the Securities
Exchange Act of 1934, as amended, that the Schedule 13D to which this Agreement
is attached as an Exhibit (the "Schedule 13D"), and any amendments thereto, will
be filed with the Securities and Exchange Commission jointly on behalf of the
undersigned. This Agreement may be signed by the undersigned in separate
counterparts.

Dated: April 15, 1999

                                    APTCO GEN-PAR, L.L.C.

                                    By: /s/ ▇▇▇▇▇▇▇ ▇▇▇▇▇
                                        -----------------
                                        Name: ▇▇▇▇▇▇▇ ▇▇▇▇▇
                                        Title: Authorized Signatory


                                    APTCO HOLDINGS, L.L.C.

                                    By: /s/ ▇▇▇▇▇▇▇ ▇▇▇▇▇
                                        -----------------
                                        Name: ▇▇▇▇▇▇▇ ▇▇▇▇▇
                                        Title: Authorized Signatory


                                    THE BERKSHIRE COMPANIES LIMITED
                                    PARTNERSHIP

                                    By: KGP-1, Inc.,
                                        its General Partner

                                        By: /s/ ▇▇▇▇▇▇▇ ▇▇▇▇▇
                                            -----------------
                                            Name: ▇▇▇▇▇▇▇ ▇▇▇▇▇
                                            Title: President

                                    KGP-1, INC.

                                    By: /s/ ▇▇▇▇▇▇▇ ▇▇▇▇▇
                                        -----------------
                                        Name: ▇▇▇▇▇▇▇ ▇▇▇▇▇
                                        Title: President


                                                                               2

                                    KGP-2, INC.

                                    By: /s/ ▇▇▇▇▇▇▇ ▇▇▇▇▇
                                        -----------------
                                        Name: ▇▇▇▇▇▇▇ ▇▇▇▇▇
                                        Title: President


                                    /s/ ▇▇▇▇▇▇▇ ▇▇▇▇▇
                                    -----------------
                                    ▇▇▇▇▇▇▇ ▇▇▇▇▇


                                            *
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                                    * By: /s/ ▇▇▇▇▇▇▇ ▇▇▇▇▇
                                          -----------------
                                          Name:  ▇▇▇▇▇▇▇ ▇▇▇▇▇
                                          Title: Attorney-in-fact