( 1 ) THE appellant, M/s. Jiyajeerao Cotton Mills Ltd. , a public company, derived profits and gains from several industries owned by it, one of which was a chemical factory known as Saurashtra Chemicals, situate at Porbander, where during the previous year relevant to the assessment year 1966-67, soda ash was manufactured.

( 2 ) THERE is no dispute that soda ash is one of the items mentioned in Part III of the First Schedule to the Finance Act, 1965, and the appellant was, therefore, entitled to a special rebate of 35 per cent. on the profits and gains attributable to the business of manufacture and production of soda ash under Paragraph F of Part I of the First Schedule to the Finance Act, 1965.

( 3 ) THE appellant had at first filed its income-tax return for the assessment year 1966-67, without claiming the said special rebate under Paragraph F of Part I of the First Schedule to the Finance Act, 1965, in respect of its profits and gains attributable to the business of manufacture and production of soda ash in Saurashtra Chemicals but subsequently filed a revised return claiming such rebate.

( 4 ) ON or about the 27th February, 1970, respondent No. 1 completed the assessment under Section 143 (3)of the I. T. Act, 1961, whereby the overall total income of the appellant was computed at Rs. 2,21,29,146 after allowing development rebate on all the said three industries including Saurashtra Chemicals. Respondent No. 1 also allowed the special rebate of 35 per cent, on the profits and gains attributable to the business of manufacture and production of soda ash under Paragraph F of Part I of the First Schedule to the Finance Act, 1965, and in allowing such rebate made a separate computation of the profits and gains attributable to the said business at Rs. 82,20,987 as eligible for such rebate without deducting the development rebate of Rs. 5,50,040 allowed to the appellant in respect of Saurashtra Chemicals, in the computation of its overall total income as aforesaid.

( 5 ) THEREAFTER on or about the 5th May, 1972, the appellant received a notice under Section. 154/155 of the I. T. Act, 1961, issued by respondent No. 1 for amendment of the said assessment made on the 27th February, 1970, on the ground that there was a mistake apparent from the record within the meaning of Section. 154 of the said Act, the reasons whereof were noted in the said notice in the words following :"mistake in computing the profits and gains from priority industry for the purpose of tax relief--no development rebate of Rs. 5,50,040 deducted. "

( 6 ) BY a letter dated the 10th May, 1972, the appellant denied that there was any mistake apparent from the record and asserted that the mistake, if any, could be discovered only by a process of detailed reasoning and arguments on fact and law and there may be two opinions on the points involved and called upon respondent No. 1 to withdraw the said notice.

( 7 ) THEREAFTER the appellant filed a writ petition under Article 226 of the Constitution to this court challenging the said notice and a rule nisi was issued by this court. Ultimately, the said writ petition was finally heard by a single Bench of this court and by a judgment and order dated the 28th November, 1973, the said rule nisi was discharged. Hence, this appeal.

( 8 ) THE law as to what is a mistake rectifiable under Section. 154 of the I. T. Act, 1961, as being apparent from the record is well settled. A glaring and obvious mistake can be corrected under the said section but a debatable issue on the question or which required investigation and arguments as to facts or law to find out if there was a mistake cannot be rectified under the said section.

( 9 ) HERE the reason for rectification was that the development rebate of Rs. 5,50,040 allowed in the computation of the overall total income of the appellant in its assessment which was not deducted in the computation of the profits and gains attributable to the business of produc