import sys

def printfl(*args, **kwargs):
	print(*args, **kwargs)
	sys.stdout.flush()

T = int(input())

for t in range(1, T+1):
	N = int(input())
	S = [int(_) for _ in input().split()]
	
	colors_seen = set([S[0]])
	ans = [S[0]]
	
	flag = True
	for i in range(1, N):
		if S[i] == S[i-1]:
			continue
		if S[i] in colors_seen:
			flag = False
			break
		else:
			ans.append(S[i])
			colors_seen.add(S[i])
	
	if flag is False:
		ans = 'IMPOSSIBLE'
	else:
		ans = ' '.join([str(_) for _ in ans])
	
	print(f"Case #{t}: {ans}")