... by one ormore persons empowered, under national law, to auditaccounts;(d) where the firm has only one proprietor, he must makeprovision for the protection of investors in the eventof the ... the negotiations, the Commission may decide, in accordance with the procedure referred to in Article 64(2), to extend thesemeasures.4. Whenever it appears to the Commission that one of the situations referred ... obligations of the parties, and the other terms on which the firm will provide services to the client. The rights and duties of the parties to the contract maybe incorporated by reference to other documents...