T = int(input())
for case in range(1,T+1):
    N = int(input())
    Ss = list(map(int, input().strip().split()))

    last_occurrence = {}
    res = []
    for i,s in enumerate(Ss):
        if s in last_occurrence and last_occurrence[s] < i-1:
            ans = "IMPOSSIBLE"
            break
        if s not in last_occurrence: res.append(s)
        last_occurrence[s] = i
    else:
        ans = ' '.join(map(str,res))
    print(f"Case #{case}: {ans}")