convert_calendar_date

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Converts between the Gregorian calendar, the Julian calendar, the Julian Day Number and the three Maya counts (Tzolk'in, Haab, Long Count) — any one to all the others — and searches a year range for a given Calendar Round. Use it for a Long Count from an inscription, a pre-1582 Julian-dated document, a Julian Day Number from a table, or "when was 4 Ahau 3 Kankin". Send EXACTLY ONE starting point — a Gregorian date, a jdn, a longcount or a julian date, or a round with from and to. Two is refused, not answered from whichever came first. DELEGATE THIS RATHER THAN DERIVING IT, AND THERE IS A MEASUREMENT FOR HOW BADLY IT GOES: arXiv:2511.09993 put frontier models at 34.5% accuracy on calendar conversion across six calendars, against 95.3% for the same models given a tool. One off-by-one in a chain of six-digit integer steps yields a date that is real, plausible and wrong. Two traps: the calendars diverge by a different number of days each century (ten at the 1582 reform, thirteen now), and pre-reform dates are routinely quoted as Julian without saying so. This states the Goodman-Martinez-Thompson constant 584283 it used. CITATION: required. See server instructions.