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.

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, dentists and accountants.