#define  _CRT_SECURE_NO_WARNINGS
#pragma comment (linker, "/STACK:526000000")

#include "bits/stdc++.h"

using namespace std;
typedef string::const_iterator State;
#define eps 1e-11L
#define MAX_MOD 1000000007LL
#define GYAKU 500000004LL

#define MOD 998244353LL
#define seg_size 262144*2LL
#define pb push_back
#define mp make_pair
typedef long long ll;
#define REP(a,b) for(long long (a) = 0;(a) < (b);++(a))
#define ALL(x) (x).begin(),(x).end()

unsigned long xor128() {
	static unsigned long x = 123456789, y = 362436069, z = 521288629, w = time(NULL);
	unsigned long t = (x ^ (x << 11));
	x = y; y = z; z = w;
	return (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)));
}

void init() {
	iostream::sync_with_stdio(false);
	cout << fixed << setprecision(20);
}

#define int ll

void solve() {
	while (true) {
		int n, t, l, b;
		cin >> n >> t >> l >> b;
		if (n == 0) return;
		int inst[200] = {};
		REP(i, l) {
			int a;
			cin >> a;
			inst[a] = 1;
		}
		REP(i, b) {
			int a;
			cin >> a;
			inst[a] = 2;
		}
		long double ans[200][200] = {};
		ans[0][0] = 1.0;
		REP(i, t) {
			REP(q, n) {
				long double prob = ans[i][q] / (long double)6.0000L;
				for (int j = 1; j <= 6; ++j) {
					int next = q + j;
					if (next > n) {
						next = n - (next - n);
					}
					if (inst[next] == 1) {
						ans[i + 2][next] += prob;
					}
					else if (inst[next] == 2) {
						ans[i + 1][0] += prob;
					}
					else {
						ans[i + 1][next] += prob;
					}
				}
			}
			ans[i + 1][n] += ans[i][n];
		}
		cout << ans[t][n] << endl;
	}
}

#undef int
int main() {
	init();
	solve();
}
