Rectification of mistake.
(a) amend any order passed by it under the provisions of this Act ;
5[(1A) Where any matter6 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.]
(2) 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 for rectifying any such mistake which has been brought to its notice by the assessee, and where the authority concerned is the 7[***] 8[Commissioner (Appeals)], by the 9[Assessing] Officer also.
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(3) 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.
(4) Where an amendment is made under this section, an order shall be passed in writing by the income-tax authority concerned.
(6) Where any such amendment has the effect of enhancing the assessment or reducing a refund already made, the 11[Assessing] Officer shall serve on the assessee a notice of demand in the prescribed form specifying the sum payable12-13, and such notice of demand shall be deemed to be issued under section 156 and the provisions of this Act shall apply accordingly.
(7) Save as otherwise provided in section 155 or sub-section (4) of section 186 no amendment under this section shall be made after the expiry of four years 14[from the end of the financial year in which the order14a sought to be amended was passed.]
15[(8) Without prejudice to the provisions of sub-section (7), where an application for amendment under this section is made by the assessee on or after the 1st day of June, 2001 to an income-tax authority referred to in sub-section (1), the authority shall pass an order, within a period of six months from the end of the month in which the application is received by it,—
(a) making the amendment; or
(b) refusing to allow the claim.]