title: BigInteger copying
body: <p>Maybe I'm really confused because it seems a very simple question but Google and the official documentation were not enough.</p>
  
  <p>I want to copy an BigInteger, and I can't find a clean way of doing it. <code>BigInteger a = b</code> when <code>b</code> is a BigInteger, as BigInteger is an object and there's no operator overloading here, <code>a</code> references to the same object as <code>b</code></p>
  
  <p>The cleanest way I've found so far is <code>BigInteger a = b.add(BigInteger.ZERO)</code>, but still a dirty way for me.</p>