Secession is neither a Legislative nor Judicial Act. Secession is not a document. "Proving an Act" pursuant to Art 4, Sec 1, involves a showing that a document provided for use in court is authentic. For a Legislative Act, affixation of the official seal of the state is the prescribed method to "Prove an Act." The Congress not only MAY prescribe laws for states to prove their acts, CONGRESS ENACTED SUCH LAWS.
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United States Code
TITLE 28 - JUDICIARY AND JUDICIAL PROCEDURE
PART V - PROCEDURE
CHAPTER 115 - EVIDENCE; DOCUMENTARY
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U.S. Code as of: 01/22/02
Section 1738. State and Territorial statutes and judicial proceedings; full faith and credit
The Acts of the legislature of any State, Territory, or Possession of the United States, or copies thereof, shall be authenticated by affixing the seal of such State, Territory or Possession thereto.
The records and judicial proceedings of any court of any such State, Territory or Possession, or copies thereof, shall be proved or admitted in other courts within the United States and its Territories and Possessions by the attestation of the clerk and seal of the court annexed, if a seal exists, together with a certificate of a judge of the court that the said attestation is in proper form.
Such Acts, records and judicial proceedings or copies thereof, so authenticated, shall have the same full faith and credit in every court within the United States and its Territories and Possessions as they have by law or usage in the courts of such State, Territory or Possession from which they are taken.
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The Act of May 26, 1790 (1 Stat. 122) states
"Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled,
That the acts of the legislatures of the several states shall be authenticated by having the seal of their respective states affixed thereto:
That the records and judicial proceedings of the courts of any state, shall be proved or admitted in any other court within the United States, by the attestation of the clerk, and the seal of the court annexed, if there be a seal, together with a certificate of the judge, chief justice, or presiding magistrate, as the case may be, that the said attestation is in due form."