I reject any such narrow interpretation. The definition of assessment in s. 6(1) may, in my view, quite appropriately be applied to the word where it appears in s. 264(1) (b). I can discern no intention to the contrary; indeed even in the absence of any definition of "assessment", the use of the word in par. (b) appears to me to be one descriptive of the entire process whereby, from the interaction of taxable income and allowable deductions, there first emerges a taxpayer's taxable income, from which his tax may then be calculated and notified to him. In R. v. Deputy Federal Commissioner of Taxation (S.A.); Ex parte Hooper [1] , Isaacs J. referred to part of this process as "the Commissioner's ascertainment, on consideration of all relevant circumstances, including sometimes his own opinion, of the amount of tax chargeable to a given taxpayer"; see also Batagol v. Federal Commissioner of Taxation [2] , per Kitto J. [3] , and per Owen J. [4] . It is evidence which may bear upon that process and which, by casting light upon some relevant fact, may affect this "consideration of all relevant circumstances" by the Commissioner that a person can be required to give under par. (b). It will extend to evidence as to whether or not an outgoing has in fact been incurred and, if it has, whether it constitutes an allowable deduction, for, as Dixon J. said in Richardson v. Federal Commissioner of Taxation [5] , "In ascertaining the taxable income for the purpose of assessment, the questions must be dealt with whether assessable income has been omitted from, or excessive deductions have been included in, a return."