(6) Notwithstanding the provisions of paragraph (5), gains from the alienation of any property derived by an individual who has been a resident of a Contracting State and who has become a resident of the other Contracting State, may be taxed in the first-mentioned State if the alienation of the property occurs at any time during the four years next following the date on which the individual has ceased to be a resident of the firstmentioned State. Independent personal services (1) Income derived by a resident of a Contracting State in respect of professional services or other activities of an independent character shall be taxable only in that State except in the following circumstances, when such income may be taxed in the other Contracting State: (a) if he has a fixed base regularly available to him in the other Contracting State for the purpose of performing his activities; in that case only so much of the income as is attributable to that fixed base may be taxed in the other State; or (b) if his stay in the other State is for a period or periods aggregating 183 days or more in any twelve month period commencing or ending in the fiscal year concerned; in that case, only so much of the income as is derived from his activities performed in that other State may be taxed in that other State. (2) The term " professional services " includes especially independent scientific, literary, artistic, educational or teaching activities as well as the independent activities of physicians, lawyers, engineers, architects, surgeons, dentists and accountants. Dependent personal services