Part on "Model Theory"

[rzach]

The part on model theory has very nice proofs of interpolation/definability and Lindström's theorem, but the earlier sections on basics of model theory have to be expanded significantly, both in terms of coverage and in terms of the presentation of what's already there: much more explanation and motivation.

[aarana]

I am teaching a yearlong master-level sequence in model theory this year ; thus I am teaching the basics as well. I am happy to handle the model theory section, therefore.