#include<iostream>
#include<cstdio>
#include<string>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
using namespace std;
typedef long long ll;
const ll MOD = 1000000007;
const ll INF = (ll)1000000007 * 1000000007;
const double EPS = 1e-9;
typedef pair<int, int> P;
typedef unsigned int ui;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
int main() {
	int n, t, l, b;
	while (cin >> n >> t >> l >> b, n) {
		int marked[101] = {};
		int x=0;
		rep(i, l) {
			cin >> x; marked[x] = 1;
		}
		rep(i, b) {
			cin >> x; marked[x] = -1;
		}
		double p[101] = {};
		p[0] = 1;
		double q[101] = {};
		double u[101] = {};
		double sum = 0;
		rep(i, t) {
			rep(j, n + 1) {
				rep1(k, 6) {
					int r = j + k;
					if (r > n) {
						r = 2 * n - r;
					}
					if (marked[r] == -1) {
						q[0] += p[j] / (double)6;
					}
					else if (marked[r] == 1) {
						u[r] += p[j] / (double)6;
					}
					else {
						q[r] += p[j] / (double)6;
					}
				}
			}
			rep(j, n + 1) {
				p[j] = q[j];
			}
			rep(j, n + 1) {
				q[j] = u[j];
			}
			rep(j, n + 1) {
				u[j] = (double)0;
			}
			sum += p[n];
			p[n] = (double)0;
		}
		cout << fixed << setprecision(6) << sum << endl;
	}
	return 0;
}
