9. Reassessment
If, after a person liable to pay tax has been assessed under Section 8 for any period, the assessing authority has reason to believe that any purchase value or part thereof has, in respect of that period, escaped assessment or has been under assessed or assessed at a lower rate, then the assessing authority may within four years from the date of the order of assessment of the particular period and after giving the person a reasonable opportunity of being heard; reassess the tax due from him and may direct him to pay in addition to the tax so assessed, penalty as specified in sub-section (1) of Section 18.