for t in range(int(input())):
    p = int(input())
    s = input().split()

    # Check if Badari can win
    possible = True
    for i in range(p-1):
        if sorted(s[i]) > sorted(s[i+1]):
            possible = False
            break

    # Output the result
    if possible:
        print("Case #{}: POSSIBLE".format(t+1))
        print(" ".join("".join(sorted(part)) for part in s))
    else:
        print("Case #{}: IMPOSSIBLE".format(t+1))