HashSet<String> mut = Sets.intersection(friends, enemies).copyInto(new HashSet<String>());

    enemies.add("Joe");
    assertEquals(2, frenemies.size());
    assertEquals(1, immut.size());
    assertEquals(1, mut.size());
  }

  public void testDifference() {
    Set<String> friends = Sets.newHashSet("Tom", "Joe", "Dave");
    Set<String> enemies = Sets.newHashSet("Dick", "Harry", "Tom");

    HashSet<String> mut = Sets.intersection(friends, enemies).copyInto(new HashSet<String>());

    enemies.add("Joe");
    assertEquals(2, frenemies.size());
    assertEquals(1, immut.size());
    assertEquals(1, mut.size());
  }

  public void testDifference() {
    Set<String> friends = Sets.newHashSet("Tom", "Joe", "Dave");
    Set<String> enemies = Sets.newHashSet("Dick", "Harry", "Tom");

Habernal, Jakub Lipinski, Jacky, Jason Zaman, Jason Zavaglia, jayhpark530,
jcf94, jefby, Jeff Daily, Jeff Poznanovic, Jeffrey Poznanovic, Jekyll Lai, jer,
Jeroen BéDorf, jerryyin, jhalakp, jiakai, Jia Qingtong, Jiankang, JiangXIAO, Joe
Bowser, Joe Q, Joe Quadrino, Joel Shapiro, Johan Gunnarsson, Jojimon Varghese,
Jonas Rauber, Jonathan Kyl, Jonathan, Joon, Joppe Geluykens, Joseph Friedman,
Josh Beal, jtressle, Julian Niedermeier, Junqin Zhang, Justin Dujardin, Justin

Given the function and calls
</p>
<pre>
func Greeting(prefix string, who ...string)
Greeting("nobody")
Greeting("hello:", "Joe", "Anna", "Eileen")
</pre>

<p>
within <code>Greeting</code>, <code>who</code> will have the value
<code>nil</code> in the first call, and
<code>[]string{"Joe", "Anna", "Eileen"}</code> in the second.
</p>

<p>
If the final argument is assignable to a slice type <code>[]T</code> and

Given the function and calls
</p>
<pre>
func Greeting(prefix string, who ...string)
Greeting("nobody")
Greeting("hello:", "Joe", "Anna", "Eileen")
</pre>

<p>
within <code>Greeting</code>, <code>who</code> will have the value
<code>nil</code> in the first call, and
<code>[]string{"Joe", "Anna", "Eileen"}</code> in the second.
</p>

<p>
If the final argument is assignable to a slice type <code>[]T</code> and