∀ (a : Std.Time.Year.Offset) (a_1 : Std.Time.Month.Ordinal) (a_2 : Std.Time.Day.Ordinal) (a_3 : a.Valid a_1 a_2),
  { year := a, month := a_1, day := a_2, valid := a_3 } = { year := a, month := a_1, day := a_2, valid := a_3 }