Boundary Rule
When a continuous interval must be assigned to named dates, a boundary rule determines the result. The event does not move, but the chosen checkpoint decides whether a date is counted, skipped, or repeated.
A Hindu-calendar festival can apparently lose a date—or occupy two. If its tithi contains no sunrise, that tithi is skipped; if it contains two sunrises, it spans two dates.
E1Sunrise turns an interval into a date
A tithi is a continuous interval, while a calendar date is a named unit. To map one onto the other, the festival rule asks whether sunrise falls inside the tithi. One sunrise produces the ordinary one-tithi, one-date match. No sunrise leaves no date to assign; two sunrises make the same tithi govern two dates. The apparent irregularity comes from imposing a discrete naming grid on a continuous cycle—the problem captured by Discretization Tradeoff.
E1Where it shows up
The missing festival date
When a tithi begins after one sunrise and ends before the next, it contains no sunrise. Under the rule, it is skipped rather than forced onto a date.
E1The repeated date
When a longer tithi contains two sunrises, the checkpoint selects it twice, so it spans two named dates.
E1The rule allocates; it does not alter
Nothing in this principle says the underlying tithi disappears, duplicates, or changes duration. “Skipped” and “repeated” describe its assignment to calendar dates. Confusing those layers creates a Reference Frame Mismatch.
E1Find the checkpoint before judging the date
When a calendar result looks missing, doubled, or displaced, write down the continuous interval and the system’s exact checkpoint—in this case, sunrise. Then count how many checkpoints fall inside the interval before treating the output as an error.
E1Episodes that teach this
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The Logic of the Hindu Calendar | Future IQ
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Festivals usually use the day whose sunrise falls inside the tithi; if a tithi contains no sunrise it is skipped, and if it contains two sunrises it spans two dates.