import sys
input = sys.stdin.readline
from collections import deque
from bisect import bisect_left, bisect_right
import itertools
#from math import *

for t in range(1, int(input())+1):

    n = int(input())
    arr = list(map(int, input().split()))
    st = set()
    ans = []
    flag = True
    for i in range(1, n):
        if arr[i] != arr[i-1]:
            if arr[i-1] in st:
                flag = False
                break
            ans.append(arr[i-1])
            st.add(arr[i-1])
    if arr[n-1] in st:
        flag = False
    else:
        ans.append(arr[n-1])
            
        
    if flag:
        print("Case #{}:".format(t), *ans)
    else:
        print("Case #{}:".format(t), "IMPOSSIBLE")