1. Adámek, J., & Trnková, V. (1990). Automata and algebras in categories (Mathematics and its applications (East European series), Vol. 37). Dordrecht: Kluwer.
2. (***)Awodey, S. (2007). Category theory (Oxford logic guides, Vol. 49). Oxford: Clarendon Press. [A nice introduction to category theory.].
3. Awodey, S., & Kishida, K. (2008). Topology and modality: The topological interpretation of first-order modal logic. The Review of Symbolic Logic, 1(Special Issue 02), 146–166.
4. Borceux, F. (1994). Handbook of categorical algebra. 1 (Encyclopedia of mathematics and its applications, Vol. 50). Cambridge: Cambridge University Press.
5. Crane, L. (2009). Relational spacetime, model categories and quantum gravity. International Journal of Modern Physics A, 24(15), 2753–2775.