∀ {leap : Bool} (ordinal : Std.Time.Day.Ordinal.OfYear leap) (idx : Std.Time.Month.Ordinal) (acc : ℤ),
  ¬↑ordinal ≤ acc + ↑(Std.Time.Month.Ordinal.days leap idx) → acc + ↑(Std.Time.Month.Ordinal.days leap idx) < ↑ordinal