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1. Income derived by an individual who is 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 such services are performed or were performed in the other Contracting State; and
a) the income is attributable to a fixed base which the individual has or had regularly available to him in that other State; or
b) such individual is present or was present in that other State for a period or periods exceeding in the aggregate 183 days in any consecutive twelve month period. In such a case the income attributable to the services 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 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, lawyers, engineers, architects, dentists and accountants.