@book{hodges_1993, place={Cambridge}, series={Encyclopedia of Mathematics and its Applications}, title={Model Theory}, DOI={10.1017/CBO9780511551574}, publisher={Cambridge University Press}, author={Hodges, Wilfrid}, year={1993}, collection={Encyclopedia of Mathematics and its Applications} } @book{maclane_1978, title={Categories for the Working Mathematics}, DOI={10.1007/978-1-4757-4721-8}, publisher={Springer New York, NY}, author={Saunders Mac Lane}, year={1978}, }