val d1 = (1983,5,28)
val d2 = (1983,9,12)
val d3 = (1983,9,10)
val d4 = (1980,10,1)
val ds = [d1,d2,d3,d4]
val ms1 = [5,9]
val ms2 = [9,11,6]
val ms3 = [1,2,3,4,6,7,8]
val ms4 = [10,5]

val is_older_t =
  [ is_older (d1,d2) = true
  , is_older (d2,d1) = false
  , is_older (d1,d1) = false
  , is_older (d3,d2) = true
  , is_older (d2,d3) = false
  , is_older (d4,d1) = true
  ]


val number_in_month_t =
  [ number_in_month (ds,5) = 1
  , number_in_month (ds,9) = 2
  , number_in_month (ds,7) = 0
  ]


val number_in_months_t =
  [ number_in_months (ds,ms1) = 3
  , number_in_months (ds,ms2) = 2
  , number_in_months (ds,ms3) = 0
  ]

val dates_in_month_t =
  [ dates_in_month (ds,5) = [d1]
  , dates_in_month (ds,9) = [d2,d3]
  , dates_in_month (ds,7) = []
  ]

val dates_in_months_t =
  [ dates_in_months (ds,ms1) = [d1,d2,d3]
  , dates_in_months (ds,ms2) = [d2,d3]
  , dates_in_months (ds,ms3) = []
  , dates_in_months (ds,ms4) = [d4,d1]
  ]

val ss1 = ["one","two","three","four","five"]

val get_nth_t =
  [ get_nth (ss1,2) = "two"
  , get_nth (ss1,1) = "one"
  ]

val date_to_string_t =
  [ date_to_string d1 = "May 28, 1983"
  , date_to_string d2 = "September 12, 1983"
  , date_to_string d3 = "September 10, 1983"
  , date_to_string d4 = "October 1, 1980"
  ]

val numbers = [1, 6, 9, 4, 2, 19]

val number_before_reaching_sum_t =
  [ number_before_reaching_sum (8, numbers) = 2
  , number_before_reaching_sum (17, numbers) = 3
  , number_before_reaching_sum (21, numbers) = 4
  , number_before_reaching_sum (1, numbers) = 0
  ]

val what_month_t =
  [ what_month 10 = 1
  , what_month 360 = 12
  , what_month 150 = 5
  , what_month 290 = 10
  , what_month 60 = 3 (* no leap years *)
  ]

val month_range_t =
  [ month_range (29,34) = [1,1,1,2,2,2]
  , month_range (20,19) = []
  , month_range (101,101) = [4]
  , month_range (304,305) = [10,11]
  ]

val oldest_t =
  [ oldest [] = NONE
  , oldest [d2] = SOME d2
  , oldest ds = SOME d4
  ]

val number_in_months_challenge_t =
  [ number_in_months_challenge (ds,ms1) = number_in_months (ds,ms1)
  , number_in_months_challenge (ds,ms2) = number_in_months (ds,ms2)
  , number_in_months_challenge (ds,ms3) = number_in_months (ds,ms3)
  , number_in_months_challenge (ds,ms1@ms1) = number_in_months (ds,ms1)
  , number_in_months_challenge (ds,ms2@ms2) = number_in_months (ds,ms2)
  , number_in_months_challenge (ds,ms3@ms3) = number_in_months (ds,ms3)
  ]

val dates_in_months_challenge_t =
  [ dates_in_months_challenge (ds,ms1) = dates_in_months (ds,ms1)
  , dates_in_months_challenge (ds,ms2) = dates_in_months (ds,ms2)
  , dates_in_months_challenge (ds,ms3) = dates_in_months (ds,ms3)
  , dates_in_months_challenge (ds,ms4) = dates_in_months (ds,ms4)
  , dates_in_months_challenge (ds,ms1@ms1) = dates_in_months (ds,ms1)
  , dates_in_months_challenge (ds,ms2@ms2) = dates_in_months (ds,ms2)
  , dates_in_months_challenge (ds,ms3@ms3) = dates_in_months (ds,ms3)
  , dates_in_months_challenge (ds,ms4@ms4) = dates_in_months (ds,ms4)
  ]

val reasonalbe_date_t =
  [ reasonable_date d1 = true
  , reasonable_date d2 = true
  , reasonable_date d3 = true
  , reasonable_date d4 = true
  , reasonable_date (~10,1,1) = false
  , reasonable_date (1900,2,29) = false
  , reasonable_date (1904,2,29) = true
  ]