New Open Logic Material on Model Theory

The Open Logic Text now comes with a part on model theory. It covers some basic definitions and results, including Cantor’s theorem that any two countable linear orders without endpoints are isomorphic and a discussion of the structure of non-standard models of arithmetic. We also have a chapter on Craig’s interpolation theorem and the Beth definability theorem as well as a chapter on Lindström’s theorem. The material comes from Aldo Antonelli’s notes. Fair warning: the material is still on the terse side; it would benefit from additional explanations, examples, motivation, and problems. We welcome suggestions for such improvements, especially if they come in the form of actual text!