def color_order(N, colors):
    assigned_values = {}
    prev_color = None
    prev_value = 0

    for color in colors:
        if color != prev_color:
            if color in assigned_values and assigned_values[color] != prev_value + 1:
                return "IMPOSSIBLE"
            assigned_values[color] = prev_value + 1
            prev_color = color
            prev_value = assigned_values[color]

    return " ".join(map(str, sorted(assigned_values.keys(), key=lambda x: assigned_values[x])))


def main():
    T = int(input())
    for t in range(1, T + 1):
        N = int(input())
        colors = list(map(int, input().split()))
        result = color_order(N, colors)
        print(f"Case #{t}: {result}")


if __name__ == "__main__":
    main()