law: 17. Rectification of mistakes.-
  (1) With a view to rectifying any mistake apparent from the record, the Commissioner, the 4[Assessing Officer], the 2[Commissioner (Appeals)] and the Appellate Tribunal may, of his, or its, own motion or on an application by the assessee in this behalf, amend any order passed by him or it in any proceeding under this Act 5[within four years from the end of the financial year in which such order was passed].
  (2) An amendment which has the effect of enhancing the assessment or reducing a refund or otherwise increasing the liability of the assessee shall not be made under this section unless the authority concerned has given notice to the assessee of its intention so to do and has allowed the assessee a reasonable opportunity of being heard.
  (3) Where an amendment is made under this section, the order shall be passed in writing by the authority concerned.
  (4) Subject to the other provisions of this Act, where any such amendment has the effect of reducing the assessment, the 4[Assessing Officer] shall make any refund which may be due to such assessee.
  (5) Where any such amendment has the effect of enhancing the assessment or reducing the refund already made, the 4[Assessing Officer] shall serve on the assessee a notice of demand in the prescribed form specifying the sum payable.