Topos theory is a subset of, for ten points, what this  eld of mathematics which deals with collections of objects and arrows, the so-called  abstract nonsense ?
A book by Guerino Mazzola connects music to this  eld of mathemat- ics. Many practitioners of this  eld refer to breaking equivalence-invariance as evil . A subset of this  eld of mathematics concerns a generalization of point- set topologies which have elementary and Grothendieck types. A fundamental result in this branch of mathematics generalizes Cayley's theorem and makes statements about   functors which are morphisms onto a  xed object; that result is the Yoneda lemma. Topos theory is a subset of, for ten points, what this  eld of mathematics which deals with collections of objects and arrows, the so-called  abstract nonsense ?
A book by Guerino Mazzola connects music to this  eld of mathemat- ics.
category theory [accept abstract nonsense before  abstract , ac- cept topos theory before  topos ]