ARTICLE 15
Independent Personal Services
(1) Income derived by a resident of one of the States in respect of professional services or other independent activities of a similar character shall be taxable only in that State unless he has a fixed base regularly available to him in the other 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 independent scientific, literary, artistic, educational or teaching activities as well as the independent activities of physicians, lawyers, engineers, architects, dentists and accountants.