alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
t = int(input())
for u in range(t):
    n = int(input())
    s = [int(i) for i in input().split()]
    cols = {}
    current = -1
    ans = []
    for col in s:
        if not col == current:
            if col in cols:
                ans = ['IMPOSSIBLE']
                break
            else:
                ans.append(str(col))
                cols[col] = 'hello'
                current = col
    
    ans = ' '.join(ans)
    
    print('Case #' + str(u+1) + ':', ans)