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Mathematics Research Blog

Articles on category theory, universal algebra, topology, and the cultures around mathematics.

Tarski's automorphisms

Notes on Alfred Tarski’s 1966 lecture “What are logical notions?” and his proposal that logical notions are precisely those invariant under all automorphisms of the universe of discourse, with references for further reading.

Monomorphisms and epimorphisms

Lecture-style notes on monomorphisms and epimorphisms: closure under composition, split morphisms, and how Choice makes Set epis split, with examples.

hom-Sets

Hom-sets worked out in any category: hom-functors preserve identities and composition, and detect monos/epis by injectivity - notes for Lean 4 formalisation.

Describing difficult spaces

A guide to describing and visualizing complex topological spaces such as tori, Klein bottles, and Möbius strips using gluing diagrams and geometric intuition. Explores identification spaces.

Free semimodules and their examples

Honours project on free semimodules and their examples. Covers definitions, universal properties, and connections to category theory and universal algebra. Supervised by Prof. G. Janelidze (UCT).

M-sets and Yoneda for monoids

Yoneda lemma for monoids via M-sets: explicit Nat(M(-), X) <-> X bijection, Cayley as a corollary, plus Yoneda embedding and an enriched remark for self-study.