The International Standard Day Calendar (ISDC) is a subset of the International Standard Calendar (ISC), hence a standardized variant of the proleptic Gregorian calendar (PGC), more specifically ordinal days of the year (DoY). The International Day Calendar (IDC) is an expansion of the ISDC. It runs in parallel with the International Standard Month Calendar (ISWC) and is an alternative representation of the same year with the leap day at the end of the year, i.e. -366, instead of at the end of the second month, i.e. -02-29. 

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