import sys, math, itertools, functools, collections
input = sys.stdin.readline

def solve(testcase):
    n = int(input())
    a = [*map(int, input().split())]
    b = [(i, len(list(j))) for i, j in itertools.groupby(a)]
    res = 'IMPOSSIBLE'
    if len(set(i[0] for i in b)) == len(b):
        res = ' '.join(str(i[0]) for i in b)
    print('Case #'+str(testcase)+':', res)


for testcase in range(1, int(input())+1):
    solve(testcase)