import fileinput
import sys

sys.setrecursionlimit(10**6)

lines = fileinput.input()

def read(conv=str, sep=None):
    global lines
    line = lines.readline().strip()
    if sep is None:
        return conv(line)
    else:
        return [conv(token) for token in line.split(sep)]

def eprint(*args, **kwargs):
    print(*args, file=sys.stderr, **kwargs)

def solve(N, S):
    order = []
    assigned = set()
    for i, s in enumerate(S):
        if i-1 >= 0 and S[i-1] == s:
            # same block
            continue
        if s in assigned:
            # block in between
            return None
        else:
            # assign new
            order.append(s)
            assigned.add(s)
    return order

T = read(int)
for t in range(T):
    N = read(int)
    S = read(int, ' ')
    sol = solve(N, S)
    if sol is None:
        print("Case #{0}:".format(t + 1), "IMPOSSIBLE")
    else:
        print("Case #{0}:".format(t + 1), *sol)