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Works placed in the public domain by the creators.
Procedures, facts and ideas, methods of operation, and concepts are included in the public domain. These are not protected by copyright.
Works whose copyright has expired.
Works published before Jan. 1, 1926, are in the public domain. January 1st of each new year we gain more items in the public domain since the works were published more than 95 years ago and copyright has expired.
Works that have chosen a CC0 Creative Commons license.