Determination of tax evasion: notice, interest and penalty regime for fraud, willful misstatement or suppression of facts. Where tax is unpaid, short paid, erroneously refunded, or input tax credit wrongly availed by reason of fraud, wilful misstatement or suppression of facts, the proper officer shall serve a notice requiring payment of tax, interest under section 50 and a penalty equal to the tax. The officer may issue supplementary statements for related periods, voluntary pre-notice payment with reduced penalty bars notice for that amount, and staged payments after notice or order conclude proceedings; the officer must determine and issue an order within the five-year limitation period.