title: find candidate key from fd
body: <p>Hi I need a little help with finding <strong>candidate key</strong> with FD:</p>
  <p>given relation : R{x,y,z,s,t,u,w}</p>
  <p>FD: {s-&gt;x , t-&gt;y , x-&gt;y ,xy-&gt;tuz}</p>
  <p>is the candidate key {s,w} ?</p>