I have completed a course on Discrete Mathematics and really enjoyed studying the chapter on relations. In fact I went back and finished what we hadn't covered in class. I did basic stuff like n-ary relations , representations of relations, closure of relations, equivalence of relations and partial ordering.
I'm an undergraduate and was hoping to get recommendations for online sources and books which discuss more advanced topics on relations.
Or are relations studied under some other field like categorical theory? Any how if you can't think of a specific book, what are some topics and theorems, or books for related topics(other functions) you could point me in the direction of? Thanks a lot and appreciate it.