The MRDP theorem

I gave a rough-and-ready talk yesterday, introducing the MRDP theorem to some logic-minded philosophers (mostly postgrads). The aim was to explain what the theorem says and why it is interesting, rather than to talk about the proof in detail. Here's a slightly tidied version of my rough-and-ready handout.

I don't pretend to know a great deal about this stuff, so I'd like to hear about needed corrections: and suggestions for improvements and additions will be most welcome too.