Maintenance of books for presumptive taxpayers required when they opt out or claim profits below deemed amounts. Maintenance of books of account is required where a presumptive taxpayer discontinues the scheme after having opted it in any of the preceding five years and, for persons under the presumptive provisions 44AE, 44BB and 44BBB, where the taxpayer claims actual profits lower than the deemed profits computed under those provisions. The obligation thus arises both on opting out after recent use and on asserting profits below statutory deemed levels.