Optional concessional corporate tax rate available to domestic companies subject to specified deduction and carry forward restrictions. A domestic company may opt into a concessional tax rate by a prescribed, irrevocable election filed by the return due date; the election excludes numerous specified deductions (notably most Chapter VI-A provisions), bars carry forward or set off of losses and unabsorbed depreciation attributable to those exclusions, requires depreciation to be claimed under the general depreciation provision as prescribed, and mandates corresponding written down value adjustments where prior depreciation was not fully given effect. A qualifying IFSC Unit may preserve its specific deduction subject to its conditions.