def solution():
    N = int(input().strip())
    S = list(map(int, input().strip().split()))
    result = []
    lookup = {}
    for i, x in enumerate(S):
        if x not in lookup:
            result.append(x)
        elif lookup[x] != i-1:
            return "IMPOSSIBLE"
        lookup[x] = i
    return " ".join(map(str, result))

for case in range(int(input())):
    print('Case #%d: %s' % (case+1, solution()))