from typing import Dict, Any


class SolutionBase:
    # internal code for
    @staticmethod
    def read_int():
        return int(input())

    @staticmethod
    def read_ints():
        return [int(i) for i in input().split()]

    @staticmethod
    def read_line():
        return input().strip()

    # implementation in subclass
    def load_data(self) -> Dict[str, Any]:
        raise NotImplementedError

    def solve(self, **kwargs):
        raise NotImplementedError

    def format_answer(self, answer) -> str:
        raise NotImplementedError

    def main(self):
        t = self.read_int()
        for i in range(1, t+1):
            answer = self.format_answer(
                self.solve(
                    **self.load_data()
                )
            )
            print(f"Case #{i}: {answer}")


class MySolution(SolutionBase):
    def load_data(self) -> Dict[str, Any]:
        card_count = self.read_int()
        card_list = self.read_ints()
        return {
            'card_count': card_count,
            'card_list': card_list
        }

    def solve(self, card_count, card_list):
        prev = 0
        done = set()
        answer = []
        for card in card_list:
            if prev == card:
                continue
            else:
                prev = card
                if card in done:
                    return
                answer.append(card)
                done.add(card)
        return answer

    def format_answer(self, answer) -> str:
        if answer:
            return " ".join(map(str, answer))
        else:
            return "IMPOSSIBLE"


if __name__ == "__main__":
    MySolution().main()