1(f)(3)(A) the amount that such CPI would have been if the annual percentage increase in CPI with respect to each year after 2019 had been 2 percentage points greater. (c) Substance taxed only once No tax shall be imposed by subsection (a) with respect to a taxable carbon substance if the person who would be liable for such tax establishes that a prior tax imposed by such section has been imposed with respect to such product. (d) Exemption for exports (1) Tax-free sales (A) In general No tax shall be imposed under subsection (a) on the sale by the manufacturer or producer of any taxable carbon substance for export or for resale by the purchaser to a second purchaser for export. (B) Proof of export required Rules similar to the rules of section 4221(b) shall apply for purposes of subparagraph (A). (2) Credit or refund where tax paid (A) In general Except as provided in subparagraph (B), if— (i) tax under subsection (a) was paid with respect to any taxable carbon substance, and (ii) (I) such substance was exported by any person, or (II) such substance was used as a material in the manufacture or production of a taxable carbon substance which was exported by any person and which, at the time of export, was a taxable carbon substance, credit or refund (without interest) of such tax shall be allowed or made to the person who paid such tax. (B) Condition to allowance No credit or refund shall be allowed or made under subparagraph (A) unless the person who paid the tax establishes that he— (i) has repaid or agreed to repay the amount of the tax to the person who exported the taxable carbon substance, or (ii) has obtained the written consent of such exporter to the allowance of the credit or the making of the refund. (C) Refunds directly to exporter The Secretary shall provide, in regulations, the circumstances under which a credit or refund (without interest) of the tax under subsection (a) shall be allowed or made to the person who exported the taxable carbon substance, where— (i) the person who paid the tax waives