Rectification of mistake.12. (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)
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may make an amendment under sub-section (1) of its own motion, and
(b)
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shall make such amendment if any mistake is brought to its notice,-