@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},
}