ἐν δὲ μηνὸς πρῶτον τύχεν ἆμαρ → it chanced to be on the first of the month, that day fell on the first of the month
inf. ao.2 Moy. de ἔχω.
σχέσθαι: inf. aor. 2 med. к ἔχω.
