21. In this division, the expression:(a) “partner” means a person who, because he was a member of a partnership on 31 December 1971 and was a member without interruption from 18 June 1971 or from the creation of the partnership if it was created subsequently, could reasonably be deemed as having had an interest in the property of the partnership on 31 December 1971;
(b) “acquisition cost” of depreciable property of a prescribed class belonging to a partnership on 31 December 1971 for a person who was member of it on that date means the aggregate of the undepreciated capital cost to such person of the property of such class on 31 December 1971 and of the total depreciation allowed to him before 1972 on the property of such class;
(c) “undepreciated capital cost of any class of depreciable property to the partnership” means the lesser amount obtained after having multiplied, for each partner, the reciprocal of his percentage of interest in property of that class by the excess of the undepreciated capital cost of such property to him on 31 December 1971 over the amount determined under paragraph a of section 25;
(d) “percentage of interest” of a member of a partnership in any depreciable property of a prescribed class owned by the partnership on 31 December 1971 means the proportion expressed as a percentage that the interest of such partner in property of that class is of the aggregate of the interests of all the members in the property of that class on such date.