#include "bits/stdc++.h"
using namespace std;
#define int long long
int mod=1e9+7;

signed main(){
  while(true){
    int n,t,l,b;
    cin>>n>>t>>l>>b;
    if(n==0&&t==0&&l==0&&b==0)break;
    vector<int> ms(n+1,0);
    for(int i=0;i<l;i++){
      int a;
      cin>>a;
      ms[a]=1;
    }
    for(int i=0;i<b;i++){
      int a;
      cin>>a;
      ms[a]=2;
    }
    vector<vector<double> > dp(t+2,vector<double>(n+1,0));
    dp[0][0]=1;
    for(int i=0;i<t;i++){
      for(int j=0;j<n;j++){
        if(dp[i][j]==0)continue;
        for(int k=1;k<=6;k++){
          int np=j+k;
          if(np>n)np=n-(np%n);
          if(ms[np]==0)dp[i+1][np]+=dp[i][j]/6;
          else if(ms[np]==1)dp[i+2][np]+=dp[i][j]/6;
          else dp[i+1][0]+=dp[i][j]/6;
        }
      }
      dp[i+1][n]+=dp[i][n];
    }
    cout<<fixed<<setprecision(20)<<dp[t][n]<<endl;
  }
}

