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 also 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 that other Contracting State; or
- (b) if his stay in the other Contracting State is for a period or periods amounting to or exceeding in the aggregate 183 days in any twelve-months period; 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 exercise of the independent activities of physicians, lawyers, engineers, architects, dentists and accountants.