Unilateral double taxation relief: lower of Indian or foreign tax rate applied to foreign-sourced income when treaty absent. Relief under Section 91 applies where an Indian resident's income arises in a country without a tax treaty, is taxed and paid abroad, and not deemed to arise in India; relief equals a deduction from Indian tax computed on the doubly taxed income at the lower of the Indian rate of tax or the foreign country's tax rate. Similar relief is available to non-residents assessed on a share of a firm's foreign income when foreign tax is paid. Computation requires aggregating income, computing tax and an average Indian rate, comparing it with the foreign rate actually paid, and applying the lower rate to the foreign income.