MENON, J.

The petitioners are assessees under the Kerala General Sales Tax Act, 1963. Section 18 of the Act providing for "provisional assessment" was omitted from the statute with effect from 1st April, 1982 by the Kerala General Sales Tax (Amendment) Act, 1983 (Act 3 of 1983). The Rules framed under the statute were also amended to give effect to this change in policy, but sub-rules (7) to (14) of rule 21, authorising provisional monthly assessments, were retained with some minor modifications. And the contention of the petitioners is that these sub-rules cannot validly operate after 1st April, 1982 in view of the deletion of section 18. The sub-rules are ultra vires the statute as it now stands, it is contended.

2. Ignoring details relating to classification of dealer, rates of tax and other matters, section 5 of the K.G.S.T. Act requires every dealer to pay tax on his taxable turnover for a year. Purchase tax under section 5A is also geared to the taxable turnover for a year. "Turnover" means the aggregate amount for which goods are either bought or sold; and "taxable turnover" means the turnover on which tax is payable, after permissible deductions. Section 16(1) in C