It is an anonymous work or pseudonymous work and 50 years have passed since the date of its publication (or creation, whatever date is the latest)
It is a collective or audiovisual work and 50 years have passed since the date of its publication (or creation, whatever date is the latest)
It is another kind of work, and 50 years have passed since the year of death of the author (or last-surviving author)
It is one of "laws, legislative decrees, decrees and decisions issued by all public authorities and official translations thereof"
You must also include a United States public domain tag to indicate why this work is in the public domain in the United States. Note that this work might not be in the public domain in countries that do not apply the rule of the shorter term and have copyright terms longer than life of the author plus 50 years. In particular, Mexico is 100 years, Jamaica is 95 years, Colombia is 80 years, Guatemala and Samoa are 75 years, Switzerland and the United States are 70 years, and Venezuela is 60 years.
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