#include <bits/stdc++.h>

using namespace std;

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second

typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PII;
typedef double db;

int n, k;

void dfs(int v, const vector<VI>& g, VI& used, VI& order)
{
	used[v] = 1;
	for (int to : g[v])
	{
		if (!used[to])
			dfs(to, g, used, order);
	}
	order.PB(v);
}

void solve()
{
	vector<vector<VI>> g(3, vector<VI>(2 * n));
	// x[2 * i] = l[i], x[2 * i + 1] = r[i]
	FOR(i, 0, n)
	{
		FOR(p, 0, 3)
		{
			// l[i] < r[i]
			g[p][2 * i + 1].PB(2 * i);
		}
	}
	while (k--)
	{
		char t;
		int i, j;
		cin >> t >> i >> j;
		i--;
		j--;
		if (t == 'I')
		{
			FOR(p, 0, 3)
			{
				// l[i] < r[j], l[j] < r[i]
				g[p][2 * j + 1].PB(2 * i);
				g[p][2 * i + 1].PB(2 * j);
			}
		}
		else
		{
			// r[i] < l[j]
			g[t - 'X'][2 * j].PB(2 * i + 1);
		}
	}
	vector<VI> vals(3, VI(2 * n));
	bool ok = true;
	FOR(p, 0, 3)
	{
		VI used(2 * n);
		VI order;
		FOR(i, 0, 2 * n)
			if (!used[i])
				dfs(i, g[p], used, order);
		FOR(i, 0, 2 * n)
			vals[p][order[i]] = i;
		FOR(v, 0, 2 * n)
		{
			for (int to : g[p][v])
			{
				ok &= vals[p][v] > vals[p][to];
			}
		}
	}
	if (!ok)
	{
		cout << "IMPOSSIBLE\n\n";
		return;
	}
	cout << "POSSIBLE\n";
	FOR(i, 0, n)
	{
		FOR(t, 0, 2)
		{
			FOR(p, 0, 3)
			{
				if (t > 0 || p > 0)
					cout << " ";
				cout << vals[p][2 * i + t];
			}
		}
		cout << "\n";
	}
	cout << "\n";
}

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	for (int tc = 1; ; tc++)
	{
		cin >> n >> k;
		if (n == 0 && k == 0)
			break;
		cout << "Case " << tc << ": ";
		solve();
	}
	return 0;
}