cases = int(input())

for case in range(1, cases+1):
    n = int(input())
    vals = list(map(int, input().split()))

    first_location = {}
    last_location = {}
    count = {}

    for i, v in enumerate(vals):
        if v not in first_location:
            first_location[v] = i
        last_location[v] = i
        if v not in count:
            count[v] = 0
        count[v] += 1

    bad = False
    for v in vals:
        if last_location[v] - first_location[v] != count[v] - 1:
            bad = True

    if bad:
        print(f"Case #{case}: IMPOSSIBLE")
    else:
        # sorted dict gaming
        print(f"Case #{case}: {' '.join(map(str, first_location.keys()))}")