(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.