209. If the amount the taxpayer may deduct under section 208 exceeds the amount of his tax otherwise payable under Part I of the Taxation Act (chapter I-3), for the taxation year 1981, he may deduct from his tax otherwise payable under that Part, for subsequent taxation years, an amount not exceeding the amount he could deduct for the taxation year 1981 less the aggregate of the amounts he has already deducted for previous taxation years.