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Section 9 - Limits on Congress
The privilege of the Writ of Habeas Corpus shall not be suspended, unless when in Cases of Rebellion or Invasion the public Safety may require it.
Definition of "Ex post facto":
ex post facto adj. Formulated, enacted, or operating retroactively. [Med Lat., from what is done afterwards] Source: AHD
In U.S. Constitutional Law, the definition of what is ex post facto is more limited. The first definition of what exactly constitutes an ex post facto law is found in Calder v Bull (3 US 386 ), in the opinion of Justice Chase:
1st. Every law that makes an action done before the passing of the law, and which was innocent when done, criminal; and punishes such action. 2d. Every law that aggravates a crime, or makes it greater than it was, when committed. 3d. Every law that changes the punishment, and inflicts a greater punishment, than the law annexed to the crime, when committed. 4th. Every law that alters the legal rules of evidence, and receives less, or different, testimony, than the law required at the time of the commission of the offense, in order to convict the offender.
Article 3 Section 1 - Judicial Powers
The judicial Power of the United States, shall be vested in one supreme Court, and in such inferior Courts as the Congress may from time to time ordain and establish. The Judges, both of the supreme and inferior Courts, shall hold their Offices during good Behavior, and shall, at stated Times, receive for their Services a Compensation which shall not be diminished during their Continuance in Office.