#include <iostream>
#include <sstream>
#include <string>
#include <algorithm>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <cassert>

using namespace std;

#define FOR(i,k,n) for(int i=(k); i<(int)n; ++i)
#define REP(i,n) FOR(i,0,n)
#define FORIT(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)

template<class T> void debug(T begin, T end){ for(T i = begin; i != end; ++i) cout<<*i<<" "; cout<<endl; }

typedef long long ll;
const int INF = 100000000;
const double EPS = 1e-8;
const int MOD = 1000000007;

int main(){
  int N, T, L, B;
  while(cin>>N>>T>>L>>B && N){
    bool lose[105] = {};
    bool back[105] = {};
    REP(i, L) {
      int k; cin>>k;
      lose[k] = true;
    }
    REP(i, B) {
      int k; cin>>k;
      back[k] = true;
    }
    double dp[105][105] = {};
    dp[0][0] = 1;
    REP(t, T + 1){
      REP(x, N)if(dp[t][x] > 0){
        for(int d = 1; d <= 6; d++){
          int next = x + d;
          if(next > N) next = N - (next - N);
          if(lose[next]){
            dp[t + 2][next] += dp[t][x] * 1.0 / 6.0;
          }else if(back[next]){
            dp[t + 1][0] += dp[t][x] * 1.0 / 6.0;
          }else{
            dp[t + 1][next] += dp[t][x] * 1.0 / 6.0;
          }
        }
      }
      //dp[t + 1][N] += dp[t][N];
    }
    double ans = 0;
    REP(t, T) ans += dp[t + 1][N];
    printf("%.10lf\n", ans);
    //cout<<dp[T][N]<<endl;
  }
  return 0;
}