import sys
from collections import deque, Counter
input = lambda: sys.stdin.readline().rstrip()
ii = lambda: int(input())
mi = lambda: map(int, input().split())
li = lambda: list(mi())
inf = 2 ** 63 - 1
mod = 998244353
import string

def solve(test):
    n = ii()
    s = li()
    color = [0] * (max(s) + 1)

    mex = 1

    ans = []
    b = []
    for v in s:
        if color[v] == 0:
            color[v] = mex
            ans.append(v)
            mex += 1
        b.append(color[v])
    if b != sorted(b):
        ans = 'IMPOSSIBLE'
    else:
        ans = ' '.join(map(str, ans))
    print('Case #' + str(test) + ':', ans)
        




for test in range(1, ii() + 1):
    solve(test)