Section 79, with which we are concerned, provides: "Notwithstanding anything contained in this Chapter, where a change in shareholding has taken place in a previous year in the case of a company, not being a company in which the public are substantially interested, no loss incurred in any year prior to the previous year shall be carried forward and set off against the income of the previous year unless (a) on the last day of the previous year the shares of the company carrying not less than fifty one per cent of the voting power were beneficially held by persons who beneficially held shares of the company carrying not less than fifty one per cent of the voting power on the last day of the year or years in which the loss was incurred; or (b) the Income tax Officer is satisfied that the change in the share holding was not effected with a view to avoiding or reducing any liability to tax." Section 79 is an exception to the scheme enacted in Chapter VI for the carry forward and setting off of a loss incurred in any earlier year against the income of the relevant previous year.