S. 139 : Return of income-Revised return-Export-oriented undertaking-Declaration to be furnished to Assessing Officer in writing and before due date for filing return-Filing original return on due date with Auditor’s report claiming exemption and not carrying forward any loss-Claim of exemption withdrawn in revised return filed after due date and loss claimed to be carried forward-Held to be not permissible. [S. 10B(5), 10B(8), 72, 80, 139(1), 139(3), 139(5)]