Permanent establishment rules expanded to include equipment installation and maintenance stock used for spare part replacement. The Protocol clarifies that the term 'assembly project' includes installation of equipment and that clauses on use of facilities and maintenance of stock apply mutatis mutandis where stored goods are used for delivery of spare parts or replacement components during a contract. It further provides that the Air Transport provision is to apply from an earlier effective date and allows refund of tax paid for that period upon application, and records reciprocal notifications confirming fulfilment of requirements for entry into force.