(1) United States The term United States has the meaning given such term by section 4612(a)(4). (2) Importer The term importer means the person entering the article for consumption, use, or warehousing. (3) Ton The term ton means 2,000 pounds. In the case of any taxable carbon substance which is a gas, the term ton means the amount of such gas in cubic feet which is the equivalent of 2,000 pounds on a molecular weight basis. (b) Use treated as sale If any person manufactures, produces, or imports any taxable carbon substance and uses such substance, then such person shall be liable for tax under section 4692 in the same manner as if such substance were sold by such person. (c) Special rules for inventory exchanges (1) In general Except as provided in paragraph (2), in any case in which a manufacturer, producer, or importer of a taxable carbon substance exchanges such substance as part of an inventory exchange with another person— (A) such exchange shall not be treated as a sale, and (B) such other person shall, for purposes of section 4692, be treated as the manufacturer, producer, or importer of such substance. (2) Registration requirement Paragraph (1) shall not apply to any inventory exchange unless— (A) both parties are registered with the Secretary as manufacturers, producers, or importers of taxable carbon substances, and (B) the person receiving the taxable carbon substance has, at such time as the Secretary may prescribe, notified the manufacturer, producer, or importer of such person’s registration number and the internal revenue district in which such person is registered. (3) Inventory exchange For purposes of this subsection, the term inventory exchange means any exchange in which 2 persons exchange property which is, in the hands of each person, property described in section 1221(a)(1). III Tax on certain additional imported products Sec. 4695. Imposition of tax. Sec. 4696. Imported taxable product. 4695. Imposition of tax (a) In general There is hereby imposed a tax on any imported taxable product