International Fixed Calendar (Kodak) (國際固定曆)

THE INTERNATIONAL FIXED CALENDAR — the Cotsworth plan, the twentieth century's most nearly-adopted calendar reform: thirteen months of exactly 28 days (the new month SOL wedged between June and July), YEAR DAY standing outside the week after December 28, LEAP DAY likewise blank after June 28. George Eastman championed it and EASTMAN KODAK RAN ON IT internally from 1928 to 1989; the League of Nations shortlisted it before the reform died in 1937. THE THEOREMS ARE THE CHARM, ASSERTED AT LOAD: 13×28 = 364 = 52×7, so the calendar is PERENNIAL — every month opens on Sunday and EVERY MONTH'S 13TH IS A FRIDAY (thirteen Friday-the-13ths a year, forever; the reformers considered this a feature). The Gregorian mapping's fixed points are laws: New Year shared; Year Day = 31 December always; Leap Day = 17 June exactly when the Gregorian has a 29 February; and SOL 1 = 18 JUNE IN EVERY YEAR, the invariant the blank day preserves — with the full Gregorian ↔ IFC bijection round-tripped over complete common and leap years. The rival 12-month World Calendar is NAMED, not blended. A reform served as the history it is. Pure compute, no LLM.

Cost: 1 TIAN Points per call. tRPC procedure internationalFixed.day.