Hardest Technical I've Gotten At a BB

Got this question at an interview and still don't know the answer:

Interviewer: Do asset write-ups and write-downs affect pre-tax income, or only asset write-downs? Me: Both write-ups and write-downs will affect the income statement by increasing or decreasing operating income and thus net income Interviewer: So how come asset write-ups in a merger model decrease pre-tax income? Me: Because depreciation from the write-up lowers pre-tax income Interviewer: But wouldn't the asset write-up be incorporated to increase pre-tax income? Me: .................