unique_in_order('AAAABBBCCDAABBB') == ['A', 'B', 'C', 'D', 'A', 'B'] unique_in_order('ABBCcAD') == ['A', 'B', 'C', 'c', 'A', 'D'] unique_in_order([1,2,2,3,3]) == [1,2,3]