43. In this chapter, an investment interest in a business at the end of a taxation year means, for a taxpayer who is not a corporation, the aggregate of each amount attributable to each fiscal period in Canada of such business by the taxpayer alone or in partnership and is equal:(a) in the case of the carrying on of a business by a sole proprietor, to the excess of the aggregate of the amounts that were included in computing his income for the taxation year or a previous year and were receivable at the end of the fiscal period of that business ending in the taxation year over the reserve for doubtful debts claimed by the taxpayer under section 140 of the Taxation Act (chapter I-3) for such fiscal period; or (b) in the case of the carrying on of a partnership business, to the adjusted cost base to the taxpayer of his interest in the partnership immediately after the end of the fiscal period of the partnership ending in the year.