#!/usr/bin/env python3

def solve(n, colors):
    hashmap = {}
    max_num = 0
    res = []
    for color in colors:
        if color not in hashmap:
            max_num += 1
            hashmap[color] = max_num
        elif hashmap[color] < max_num:
            return -1
        if not res:
            res.append(color)
        elif res[-1] != color:
            res.append(color)
    return ' '.join(map(str, res))


def main():
    t = int(input())
    for tc in range(1, t+1):
        n = int(input())
        colors = list(map(int, input().split()))
        res = solve(n, colors)
        res = res if res != -1 else "IMPOSSIBLE"
        print(f"Case #{tc}: {res}")


if __name__ == "__main__":
    main()