ollector decides that an object <code>obj</code> is
 is weakly-reachable, the following
 happens:

 <ul>
   <li>
     A set <code>ref</code> of references is determined. <code>ref</code> contains the
     following elements:
     <ul>
       <li>
         All weak references pointing to <code>obj</code>.
       </li>
       <li>
         All weak references pointing to objects from which <code>obj</code> is
         either strongly or softly reachable.
       </li>
     </ul>
   </li>
   <li>
     All refer