law: Expenditure-Tax Act, 1987 
  12. Rectification of mistake 
  (1) With a view to rectifying any mistake
  
  apparent from the record, the tax authority referred to in section 6 which
  
  passed any order under the provisions of this Act may, within four years of the
  
  date on which such order was passed, amend the order.
  (2) Where any matter has been considered and
  
  decided in any proceeding by way of appeal or revision relating to an order
  
  referred to in sub-section (1), the authority passing such order may,
  
  notwithstanding anything contained in any law for the time being in force,
  
  amend the order under that sub-section in relation to any matter other than the
  
  matter which has been so considered and decided.
  (3) Subject to the other provisions of this section,
  
  the authority concerned- 
  (a) may make an
  
  amendment under sub-section (1) of its own motion, and
  (b) shall make such
  
  amendment if any mistake is brought to its notice,- 
  (i) by the assessee;
  
  or
  (ii) where the
  
  authority concerned is the Commissioner (Appeals), by the 16[Assessing]
  
  Officer.
  (4) An amendment, which has the effect of
  
  enhancing an 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.
  (5) Where an amendment is made under this
  
  section, an order shall be passed in writing by the tax authority concerned.
  (6) Subject to the other provisions of this
  
  Act where any such amendment has the effect of reducing the assessment, the 16[Assessing]
  
  Officer shall make any refund which may be due to such assessee.
  (7) Where any such amendment has the effect of
  
  enhancing the assessment or reducing the refund already made, the 16[Assessing]
  
  Officer shall serve on the assessee a notice of demand in the prescribed form
  
  specifying the sum payable and such notice of demand shall be deemed to be
  
  issued under section 20 and the provisions of this Act shall apply accordingly.