156.1. A taxpayer, other than a trust, may deduct, in computing the taxpayer’s income from a business for a taxation year,(a) where the taxpayer is an individual, the proportion of the amount determined for the year in his respect under section 156.2 that the aggregate of the income earned in Québec and elsewhere by the individual for the year is of the income earned in Québec by the individual for the year;
(b) where the taxpayer is a corporation, the proportion of the amount determined for the year in its respect under section 156.3 that the aggregate of the business carried on in Canada or in Québec and elsewhere by the corporation in the year is of the business carried on in Québec by the corporation in the year.