#include <iostream>
#include <vector>
#include <map>
#include <algorithm>
using namespace std;

const string IMPOSSIBLE = "IMPOSSIBLE";

void solve(int t) {
    int n;
    cin >> n;
    vector<int> colors(n);
    for (int i = 0; i < n; i++) {
        cin >> colors[i];
    }
    map<int, int> max_seen;
    vector<int> nums(n);
    int next_num = 1;
    for (int i = 0; i < n; i++) {
        int color = colors[i];
        if (max_seen.find(color) == max_seen.end()) {
            // New color, assign a new number
            nums[i] = next_num;
            next_num++;
        } else {
            // Seen color, assign same number as before
            nums[i] = max_seen[color];
        }
        max_seen[color] = nums[i];
    }
    bool possible = true;
    for (int i = 1; i < n; i++) {
        if (nums[i] < nums[i-1]) {
            possible = false;
            break;
        }
    }
    cout << "Case #" << t << ": ";
    if (possible) {
        map<int, int> color_order;
        for (int i = 0; i < n; i++) {
            color_order[nums[i]] = colors[i];
        }
        for (auto it : color_order) {
            cout << it.second << " ";
        }
        cout << endl;
    } else {
        cout << IMPOSSIBLE << endl;
    }
}

int main() {
    int T;
    cin >> T;
    for (int t = 1; t <= T; t++) {
        solve(t);
    }
    return 0;
}