loop do
  n,t,l,b=gets.chomp.split(/ /).map{|i| i.to_i}
  break if (n|t|l|b)==0
  dice=Array.new(n+1,0)
  for i in 0..l-1
    dice[gets.chomp.to_i]=-1  #lose
  end
  for i in 0..b-1
    dice[gets.chomp.to_i]=1   #back
  end
  
  p=Array.new(n+1).map{Array.new(t+2,0)}
  p[0][0]=1
  ans=0
  for k in 1..t
    for i in 0..n-1
      for dc in 1..6
        j=i+dc
        if j>n
          j=2*n-j
        end
        if dice[j]==-1
          p[j][k+1]+=p[i][k-1]/6.0
        elsif dice[j]==1
          p[0][k]+=p[i][k-1]/6.0
          p[j][k]=0
        else
          p[j][k]+=p[i][k-1]/6.0
        end
        if j==n
          ans+=p[i][k-1]/6.0
        end
      end
    end
  end
  puts "%.6f" % ans
end