The last carbon is known as the omega carbon given by this Greek symbol omega. So we have alpha beta and then we have omega. We'll see why that's important in just a moment. Now, because to break this double bond, we actually have to input a certain amount of energy. And because the energy change symbol is given by the Greek symbol delta, this triangle, the double bond, is represented with the delta symbol. And to basically describe the position, the number of that double bond with respect to this reference point, carbon number one.