About Roman Calendar: it counts days backward and uses 3 fixed days: the Kalends (1st day of the month), the Nones (the 7th or the 5th) and the Ides (the 13th or the 15th). Each day is counted (i.e. 3 days before the Kalends of February is January 30th because they count Feb 1st, Jan 31th and Jan 30th). 'Pridie' means 'yesterday'.
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