#include <stdio.h>
#include <string.h>
#include <assert.h>

#define MAX_N (30)
#define MAX_M (20)
#define MAX_L ( 5)

#ifndef solve
#define solve solve_AC
#endif

static int N;
static int M;
static int a[MAX_M];
static int v[MAX_M];

int size(int m)
{
	m = ((m & 0xaaaaaaaa) >>  1) + (m & 0x55555555);
	m = ((m & 0xcccccccc) >>  2) + (m & 0x33333333);
	m = ((m & 0xf0f0f0f0) >>  4) + (m & 0x0f0f0f0f);
	m = ((m & 0xff00ff00) >>  8) + (m & 0x00ff00ff);
	m = ((m & 0xffff0000) >> 16) + (m & 0x0000ffff);
	return m;
}

int examine(int m)
{
	int i, w, x, y;

	w = m & a[0];
	x = 0;
	y = 1;

	while(x < y && y < M) {
		x = y;
		for(i = 1; i < M; i++) {
			if(v[i] != m && (w & a[i]) != 0) {
				v[i] = m;
				w |= m & a[i];
				y++;
			}
		}
	}

	return y == M;
}

int solve_AC(void)
{
	int m, n, x, y;

	for(n = 1; n <= MAX_L; n++) {
		for(m = (1 << n) - 1; m < (1 << N); ) {
			if(examine(m)) return m;
			x = m & ~(m - 1);
			y = m + x;
			m = (((m & ~y) / x) >> 1) | y;
		}
	}

	return 0;
}

int solve_TLE_1(void)
{
	int m, n;
	int mmin, nmin;

	nmin = MAX_L + 1;
	mmin = 0;

	for(m = 1; m < (1 << N); m++) {
		n = size(m);
		if(n < nmin && examine(m)) {
			nmin = n;
			mmin = m;
		}
	}

	return mmin;
}

int solve_TLE_2(void)
{
	int m, n;
	int mmin, nmin;
	int i, j;

	nmin = MAX_L + 1;
	mmin = 0;

	m = 0;
	n = 0;

	for(i = 1; i < (1 << N); i++) {
		j = i & ~(i - 1);
		n += (m & j) ? -1 : +1;
		m ^= j;

		if(n < nmin && examine(m)) {
			nmin = n;
			mmin = m;
		}
	}

	return mmin;
}

int main(void)
{
	char name[25][21], s[21];
	int  i, j, k, m, n;
	int  flag = 0;

	while(scanf("%d %d", &N, &M) != EOF) {
		if(N == 0 && M == 0)
			break;

		for(i = 0; i < N; i++)
			scanf("%s", name[i]);

		for(i = 0; i < M; i++) {
			a[i] = 0;
			v[i] = 0;

			scanf("%d", &n);

			for(j = 0; j < n; j++) {
				scanf("%s", s);
				for(k = 0; k < N; k++) {
					if(strcmp(s, name[k]) == 0)
						a[i] |= 1 << k;
				}
			}
		}

		m = solve();

		if(flag) putchar('\n');
		flag = 1;

		if(m == 0) {
			printf("Impossible\n");
		}
		else {
			printf("%d\n", size(m));
			for(i = 0; i < N; i++) {
				if((m & (1 << i)) != 0) puts(name[i]);
			}
		}
	}

	return 0;
}