If any non- resident person is assessed on his share in the income of a registered firm assessed as resident in India in any previous year and such share includes any income accruing or arising outside India during that previous year (and which is not deemed to accrue or arise in India) in a country with which there is no agreement under section 90 for the relief or avoidance of double taxation and he proves that he has paid income- tax by deduction or otherwise under the law in force in that country in respect of the income so included he shall be entitled to a deduction from theIndian income- tax payable by him of a sum calculated on such doubly taxed income so included at the Indian rate of tax or the rate of tax of the said country, whichever is the lower, or at the Indian rate of tax if both the rates are equal.