law: 2. Validation of State laws imposing, or authorising the imposition of, taxes on sale or purchase of goods in the course of inter-State trade or commerce.-
  Notwithstanding any judgment, decree or order of any court, no law of a State imposing, or authorising the imposition of, a tax on the sale or purchase of any goods where such sale or purchase took place in the course of inter-State trade or commerce during the period between the 1st day of April, 1951 and the 6th day of September, 1955, shall be deemed to be invalid or ever to have been invalid merely by reason of the fact that such sale or purchase took place in the course of inter-State trade or commerce; and all such taxes levied or collected or purporting to have been levied or collected during the aforesaid period shall be deemed always to have been validly levied or collected in accordance with law.
  Explanation.-In this section, 'law of a State' in relation to a State specified in Part C of the First Schedule to the Constitution, means any law made by the Legislative Assembly, if any, of that State or extended to that State by a notification issued under section 2 of the Part C States (Laws) Act, 1950 (30 of 1950).