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Re:Calculate the day of the week for any date in your head by hu3 on Wednesday January 01, 2020 @03:14PM (#21930272)
Not to mention that the ISO says Monday is day 1 of the week:

https://en.wikipedia.org/wiki/ISO_8601

Re:Calculate the day of the week for any date in your head by IgorPartola on Wednesday January 01, 2020 @04:37PM (#21930853)
But what is day 0? :)