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 unless he has a fixed base regularly available to him in the other Contracting State for the purpose of performing his activities. If he has such a fixed base, the income may be taxed in the other State but only so much of it as is attributable to that fixed base. For this purpose, where an individual who is a resident of a Contracting State stays in the other Contracting State for a period or periods exceeding in the aggregate 183 days in any twelve-month period commencing or ending in the fiscal year concerned, he shall be deemed to have a fixed base regularly available to him in that other State and the income that is derived from his activities referred to above that are performed in that other State shall be attributable to that fixed base. In such cases the income attributable to a fixed base may be taxed in that other State in accordance with principles similar to those of Article 7 for determining the amount of business profits and attributing business profits to a permanent establishment.
(2) The term "professional services" includes especially independent scientific, literary, artistic, educational or teaching activities as well as the independent activities of physicians, dentists, lawyers, engineers, architects and accountants.