#include <iostream>
#include <iomanip>
#include <cstdio>
#include <string>
#include <cstring>
#include <deque>
#include <list>
#include <queue>
#include <stack>
#include <vector>
#include <utility>
#include <algorithm>
#include <map>
#include <set>
#include <complex>
#include <cmath>
#include <limits>
#include <cfloat>
#include <climits>
#include <ctime>
#include <cassert>
using namespace std;

#define rep(i,a,n) for(int (i)=(a); (i)<(n); (i)++)
#define repq(i,a,n) for(int (i)=(a); (i)<=(n); (i)++)
#define repr(i,a,n) for(int (i)=(a); (i)>=(n); (i)--)
#define all(v) begin(v), end(v)
#define pb(a) push_back(a)
#define fr first
#define sc second
#define INF 2000000000
#define int long long int

#define X real()
#define Y imag()
#define EPS (1e-10)
#define EQ(a,b) (abs((a) - (b)) < EPS)
#define EQV(a,b) ( EQ((a).X, (b).X) && EQ((a).Y, (b).Y) )
#define LE(n, m) ((n) < (m) + EPS)
#define LEQ(n, m) ((n) <= (m) + EPS)
#define GE(n, m) ((n) + EPS > (m))
#define GEQ(n, m) ((n) + EPS >= (m))

typedef vector<int> VI;
typedef vector<VI> MAT;
typedef pair<int, int> pii;
typedef long long ll;

typedef complex<double> P;
typedef pair<P, P> L;
typedef pair<P, double> C;

int dx[]={1, -1, 0, 0};
int dy[]={0, 0, 1, -1};
int const MOD = 1000000007;
ll mod_pow(ll x, ll n) {return (!n)?1:(mod_pow((x*x)%MOD,n/2)*((n&1)?x:1))%MOD;}
int madd(int a, int b) {return (a + b) % MOD;}
int msub(int a, int b) {return (a - b + MOD) % MOD;}
int mmul(int a, int b) {return (a * b) % MOD;}
int minv(int a) {return mod_pow(a, MOD-2);}
int mdiv(int a, int b) {return mmul(a, minv(b));}

namespace std {
    bool operator<(const P& a, const P& b) {
        return a.X != b.X ? a.X < b.X : a.Y < b.Y;
    }
}

const int LOSE = 1;
const int BACK = 2;
int n, t, l, b;
double dp[110][110];
int board[110];

signed main() {
    while(cin >> n >> t >> l >> b, n || t || l || b) {
        int inp;
        memset(dp, 0, sizeof(dp));
        memset(board, 0, sizeof(board));
        dp[0][0] = 1.0;
        rep(i,0,l) cin >> inp, board[inp] = LOSE;
        rep(i,0,b) cin >> inp, board[inp] = BACK;

        repq(i,1,t) repq(j,0,n) {
            if(board[j] == LOSE) {
                int turn = min(t, i+1);
                repq(x,1,6) {
                    if(j-x >= 0) dp[turn][j] += dp[i-1][j-x] * 1.0 / 6.0;
                    if(n != j && 1 <= n+x-j && n+x-j <= 6 && n-x >= 0) dp[turn][j] += dp[i-1][n-x] * 1.0 / 6.0;
                }
            }
            else if(board[j] == BACK) {
                repq(x,1,6) {
                    if(j-x >= 0) dp[i][0] += dp[i-1][j-x] * 1.0 / 6.0;
                    if(n != j && 1 <= n+x-j && n+x-j <= 6 && n-x >= 0) dp[i][0] += dp[i-1][n-x] * 1.0 / 6.0;
                }
            }
            else {
                repq(x,1,6) {
                    if(j-x >= 0) dp[i][j] += dp[i-1][j-x] * 1.0 / 6.0;
                    if(n != j && 1 <= n+x-j && n+x-j <= 6 && n-x >= 0) dp[i][j] += dp[i-1][n-x] * 1.0 / 6.0;
                }
            }
        }
        double ans = 0.0;
        repq(i,1,t) {
            // printf("dp[%lld][%lld] = %.12lf\n", i, n, dp[i][n]);
            ans += dp[i][n];
        }
        printf("%.12f\n", ans);
    }
    return 0;
}

Measured memory_bytes: 3312