From the enumeration of the duels we know that André-Louis' first day
was a Monday (e.g., Chapter 3.IX says that Chabrillane "was killed on
Tuesday last" which was the next day). And he himself declares it
to be "some three weeks" after the death of Lagron
[Chapter 3.VII]. The only Monday on which André-Louis could
reasonably have made this statement was September 13, three weeks and
two days after the duel.