title: BigInteger.isProbablePrime
body: <p>I just want to confirm my intuition about this method. Consider the code below.</p>
  
  <pre><code>long knownPrime = // some large known prime
  int certainty = // some integer greater than 0
  
  BigInteger b = BigInteger.valueOf(knownPrime);
  boolean isPrime = b.isProbablePrime(certainty);
  </code></pre>
  
  <p>For a large known prime, and for any certainty > 0, is it accurate to say that <code>b.isProbablePrime(certainty)</code> will always return true?</p>
  
  <p>Or are there any cases where the method "guesses" that a known prime number is composite?</p>