Bad debt determination: tax officer decides on factual evidence when a bank substantiates irrecoverability. Determination whether a banking receivable is a bad debt and when it became bad is a question of fact for the income-tax officer, not the assessee's unilateral declaration. If a public bank places the facts and evidence showing irrecoverability before the I.T.O., the I.T.O. may take a reasonable view of that material in reaching a finding, subject to appeal. The treatment of audit certificates in this assessment context was considered by the Income-tax Investigation Commission (see paragraph 206).