Books of account requirement for non-specified professionals hinges on prior years' professional income or gross receipts exceeding statutory thresholds. Non-specified professionals must maintain books of account if income from the profession or gross receipts in any of the three years immediately preceding the previous year exceed the prescribed thresholds; the test applies to individuals and HUFs on one set of thresholds and to other taxpayers on a different, lower set of thresholds, with the trigger satisfied by either professional income or gross receipts in any one of those three years.