Samoa skipped a Friday in December 2011 [1]. There were 4 Fridays left so "4 or 5" still holds, but using arithmetic to calculate the number of Fridays would ha

Samoa skipped a Friday in December 2011 [1]. There were 4 Fridays left so "4 or 5" still holds, but using arithmetic to calculate the number of Fridays would have yielded a wrong answer. This is pretty uncommon with whole days so maybe less important, but thinking in this way (how can I optimize this annoying code) often leads to wrong arithmetic around hours (daylight savings and time zone changes) or seconds (leap seconds). [1] https://www.abc.net.au/news/2011-12-30/samoa-skips-friday-in-time-zone-change/3753350 https://www.abc.net.au/news/2011-12-30/samoa-skips-friday-in...