docs: public Iterator<Example> iterator()
      {
          return new Iterator<Example>()
          {
              private int index = 0;
  
              public boolean hasNext()
              {
                  return at( index ) != null;
              }
  
              public Example next()
              {
                  return at( index++ );
              }
  
              public void remove()
              {
                  throw new UnsupportedOperationException( "Specification not mutable" );
              }
          };
      }