title: are you allowed to redefine a class in ruby? or is this just in irb
body: <p>I fired up irb, and typed:</p>
  
  <p>class Point
  end</p>
  
  <p>and then I typed that again, but added some other things.</p>
  
  <p>Irb didn't complain that I was defining a class that already exists.</p>