Artikel 15

The exercise by nationals of one Contracting Party in the territory of another Party of an occupation in respect of which nationals of the latter Party are required to possess professional or technical qualifications or to furnish guarantees shall be made subject to the production of the same guarantees or to the possession of the same qualifications or of others recognised as their equivalent by the competent national authority.
Provided that nationals of the Contracting Parties engaged in the lawful pursuit of their profession in the territory of any Party may be called into the territory of any other Party by one of their colleagues for the purpose of lending assistance in a particular case.