"Marginal note:Income or loss from a source or from sources in a place4. (1) For the purposes of this Act,(a) a taxpayer???s income or loss for a taxation year from an office, employment, business, property or other source, or from sources in a particular place, is the taxpayer???s income or loss, as the case may be, computed in accordance with this Act on the assumption that the taxpayer had durin" . . . . .