Oral proof of United States or foreign unwritten law.
Section 302
SEC. 302. Oral proof of United States or foreign unwritten law. — The oral testimony of witnesses, skilled therein, is admissible as evidence of the unwritten law of the United States or of any State of the United States, or foreign country, as are also printed and published books of reports of decisions of the courts of the United States or of such State or country, or proved to be commonly admitted in such courts.