Except as otherwise provided in this subchapter, no person shall be naturalized unless he has been lawfully admitted to the United States for permanent residence in accordance with all applicable provisions of this chapter. The burden of proof shall be upon such person to show that he entered the United States lawfully, and the time, place, and manner of such entry into the United States, but in presenting such proof he shall be entitled to the production of his immigrant visa, if any, or of other entry document, if any, and of any other documents and records, not considered by the Attorney General to be confidential, pertaining to such entry, in the custody of the Service. Notwithstanding the provisions of section 405(b),1

and except as provided in sections 1439 and 1440 of this title no person shall be naturalized against whom there is outstanding a final finding of deportability pursuant to a warrant of arrest issued under the provisions of this chapter or any other Act; and no application for naturalization shall be considered by the Attorney General if there is pending against the applicant a removal proceeding pursuant to a warrant of arrest issued under the provisions of this chapter or any other Act: Provided, That the findings of the Attorney General in terminating removal proceedings or in canceling the removal of an alien pursuant to the provisions of this chapter, shall not be deemed binding in any way upon the Attorney General with respect to the question of whether such person has established his eligibility for naturalization as required by this subchapter.