code: public static boolean sameSubject(SubjectNode s1, SubjectNode s2) {
          if (s1 instanceof URIReference && s2 instanceof URIReference) {
              return sameResource((URIReference) s1, (URIReference) s2);
          } else {
              return false;
          }
      }
docs: Tells whether the given subjects are equivalent.
  <p>
  Two subjects are equivalent if they are both resources and they match
  according to the rules for resources.
  
  @param s1
  first subject.
  @param s2
  second subject.
  @return true if equivalent, false otherwise.