from sys import stdin
input = stdin.readline

def solve(n,colors):
    ans = []
    s = set()
    ans.append(colors[0])
    s.add(colors[0])
    for i in range(1,n):
        if colors[i]==colors[i-1]:
            continue
        if colors[i] in s:
            return 'IMPOSSIBLE'
        ans.append(colors[i])
        s.add(colors[i])

    return ' '.join(map(str,ans))


    

for i in range(int(input())):
    n = int(input())

    colors = list(map(int, input().split()))

    
    print(f'Case #{i+1}: {solve(n, colors)}')