#include <bits/stdc++.h>
using namespace std;

#define fi first
#define se second
#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) repl(i,0,n)
#define each(itr,v) for(auto itr:v)
#define pb(s) push_back(s)
#define mp(a,b) make_pair(a,b)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout<<#x"="<<x<<endl
#define maxch(x,y) x=max(x,y)
#define minch(x,y) x=min(x,y)
#define uni(x) x.erase(unique(all(x)),x.end())
#define exist(x,y) (find(all(x),y)!=x.end())
#define bcnt(x) bitset<32>(x).count()

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;
typedef pair<P, int> PPI;
typedef pair<ll, ll> PL;
typedef pair<P, ll> PPL;

#define INF INT_MAX/3

#define MAX_N 1000

int n,t,l,b;
int board[111];
double mem[111][111][2];

double dfs(int x,int rest,bool lose){
	if(x==n)return 1.0;
	if(rest==0)return 0.0;
	if(!lose&&board[x]==1)return dfs(x,rest-1,true);
	if(board[x]==2)return dfs(0,rest,false);
	if(mem[x][rest][lose]!=-1)return mem[x][rest][lose];
	double res=0;
	repl(i,1,6+1){
		int nx=x+i;
		if(nx<=n)res+=(1.0/6.0)*dfs(nx,rest-1,false);
		else res+=(1.0/6.0)*dfs(n-(nx-n),rest-1,false);
	}
	return mem[x][rest][lose]=res;
}

int main(){
	cin.sync_with_stdio(false);
	while(1){
		cin>>n>>t>>l>>b;
		if(n==0)break;
		memset(board,0,sizeof(board));
		rep(i,l){
			int ll;
			cin>>ll;
			board[ll]=1;
		}
		rep(i,b){
			int bb;
			cin>>bb;
			board[bb]=2;
		}
		rep(i,111)rep(j,111)rep(k,2)mem[i][j][k]=-1;
		printf("%.10f\n", dfs(0,t,false));
	}
	return 0;
}