Independent personal services: income taxable in resident State unless a fixed base or substantial presence permits other-State taxation. Income of a resident individual from professional or similar independent activities is taxable only in the State of residence, except where the individual has a fixed base in the other Contracting Party-where only income attributable to that fixed base may be taxed there-or where the individual's presence meets the treaty threshold for substantial presence, in which case only income from activities performed in that other Party may be taxed by that Party.