Category theory

1. ★★★☆☆ Introduction to category theory: a second abstraction
2. ★★★☆☆ Abstracting some categorical definitions
3. ★★★★☆ Abstracting our abstractions: limits of cones, universal properties  + examples
4. ★★★☆☆ Incredible duals
5. Anti-isomorphisms, natural isomorphisms and transformations (motivation from kernel cokernel not natural, dual not natural but double dual natural) -- https://www.quora.com/In-category-theory-what-is-an-intuitive-explanation-of-the-concept-of-natural-transformation https://www.math3ma.com/blog/what-is-a-natural-transformation
6. Functors, faithful, forgetful, concrete categories
7. Generalised elements (motivation from prob theory), object characterised by its properties, Yoneda lemma, its corollaries -- https://www.math3ma.com/blog/the-yoneda-embedding https://www.math3ma.com/blog/the-sierpinski-space-and-its-special-property
8. Stuff, structure, property; https://ncatlab.org/nlab/show/space+and+quantity
9. Theorems with our definitions: injectivity and kernels, first isomorphism theorem, rank-nullity, kernels are ideals... what special properties do we need?
10. Studying categories with category theory
11. Grothendieck