(1) The assessable income of every person for each year of income shall be ascertained after taking into account the deductions allowable under this Division.
(2) Subject to subsection (3), in ascertaining the assessable income of any person for any year of income from any source specified in section 32 there shall, upon due claims and subject to such evidence as the Comptroller may require, be allowed as a deduction, all expenditure wholly and exclusively incurred by that person during that year of income for the purpose of producing his or her assessable income from that source.
(3) For the purposes of this Division where income which has accrued to a person is considered to have accrued to, and is included in the assessable income of, some other person, any expenditure incurred by either person in relation to such income is considered to have been incurred by the person to whom such income is deemed to have accrued.
(4) Where expenditure is incurred partly for the purpose of producing assessable income and partly for purposes for which no deduction is allowable, subsection (2) shall not be construed to prevent the apportionment of such expenditure in such manner as appears to the Comptroller to be reasonable.