title: Function to determine if a set is subset of another one
body: <p>I was quite surprised that Mathematica does not provide built-in operators to determine whether a set is subset of another one.</p>
  
  <p>I mean, I have tried to find a built-in a solution to this problem but actually didn`t succeed.</p>
  
  <p>Which one is the fastest way to reach this goal in Mathematica?</p>