This circle here is the anacetal glucose amine and this square here is the Foucaults. So we have this oligosaccharide sequence known as the oligosaccharide sequence that exists on the O antigen. And we also find that on the A antigen and the B antigen. So what exactly is the difference between these three antigens? Well, it's basically the absence or presence of an additional sugar molecule. In the case of the O antigen, this is all we have.