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 the income as is attributable to that fixed base. For this purpose, where a resident of a Contracting State is present 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 any fiscal year, he shall be deemed for that fiscal year 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 deemed fixed base.

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, dentists and accountants.