@Anindya: whoops, you're right! What I should have added is that you should consider **Cost** \$$= [0,\infty]\$$ to be a symmetric monoidal preorder where the order is given by the *opposite* of the usual one. I suspect that this is also secretly what John has in mind as the definition of **Cost**. But perhaps I'm running a little ahead of the course and already giving away things that will appear in Lecture 30.