#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using VI = vector<ll>;
using VV = vector<VI>;
using VS = vector<string>;
using PII = pair<ll, ll>;

// tourist set
template <typename A, typename B>
string to_string(pair<A, B> p);

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);

string to_string(const string& s) {
  return '"' + s + '"';
}

string to_string(const char* s) {
  return to_string((string) s);
}

string to_string(bool b) {
  return (b ? "true" : "false");
}

string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}

template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}

template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}

template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")";
}

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}

void debug_out() { cerr << '\n'; }

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif
// tourist set end

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define rep(i,b) FOR(i, 0, b)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<'\n'
#define p2(s, t) cout << (s) << " " << (t) << '\n'
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << '\n'
#define p_yes() p("YES")
#define p_no() p("NO")
#define SZ(x) ((int)(x).size())
#define SORT(A) sort(ALL(A))
#define RSORT(A) sort(ALL(A), greater<ll>())
#define MP make_pair

void no(){p_no(); exit(0);}
void yes(){p_yes(); exit(0);}

const ll mod = 1e9 + 7;
const ll inf = 1e18;
const double PI = acos(-1);

ll A[200];

// i : turn
// j : pos
double dp[200][200];
void reset(){
  rep(i, 200){
    rep(j, 200){
      dp[i][j] = 0;
    }
  }
  rep(i, 200){
    A[i] = 0;
  }
}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    ll N, T, L, B;
    
    while(cin >> N >> T >> L >> B){
      if(N==0) return 0;

      reset();

      // lose one turn
      rep(i, L){
        ll a; cin >> a;
        A[a] = 1;
      }

      // return
      rep(i, B){
        ll a; cin >> a;
        A[a] = 2;
      }

      // roll a dice
      dp[0][0] = 1;
      rep(i, T){
        // ゴールだけは確率を移行
        dp[i+1][N] += dp[i][N];

        rep(pos, N){
          FOR(m, 1, 7){
            ll dst = pos+m;
            if(dst>N){
              ll surplus = dst-N;
              dst = N-surplus;
            }
        
            if(A[dst]==0){
              dp[i+1][dst] += dp[i][pos] * 1/6.0;
            }
            else if(A[dst]==1){
              dp[i+2][dst] += dp[i][pos] * 1/6.0;
            }
            else{
              dp[i+1][0] += dp[i][pos] * 1/6.0;
            }
          }
        }
      }
      double ans = dp[T][N];
      printf("%.6f\n", ans);
      // cout << setprecision(20);
      // p(ans);
    }    
    return 0;
}


Measured memory_bytes: 3424