273. An individual’s gain from disposition of land used for a farming business that he operates is, if such land includes at any time his principal residence:(a) his gain for the year from the disposition of that part of the land which does not include his principal residence, plus his gain determined for the year under section 271 as derived from the disposition of his principal residence, or
(b) if the individual so elects with respect to such land in the prescribed manner, his gain for the year from the disposition of such land including his principal residence, determined without regard to paragraph a and section 271, less the aggregate of $1,000 and $1,000 for each taxation year ending after the time referred to in the first paragraph of that section 271 during which such property was his principal residence and during which he was resident in Canada.