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UDC Classical version containing all calendars.
UDC Archaic Contains all calendars not longer in used, e.g. French Republic calendars, Mayan calendar, Soviet calendar, ...
UDC Japan Japanese Gregorian, Jimmu Tenno and Nengo calendars.
UDC Reform All reform calendars, i.e. propositions to replace existing calendars, such as the Gregorian calendar.
UDC Islamic List of islamic calendars, or calendars having a relationship with them.