Jeffery Mensah

This post builds off of Roger Penrose's article On the Cohomology of Impossible Figures, in which he shows a remarkable connection betweeen impossible drawings, such as the Penrose triangle, and nontrivial cohomology groups...

The snake lemma is a fundamental tool of homological algebra which is primarily used in the construction of the homology long exact sequence. It's proof, like many others in homological algebra, is an exercise in diagram chasing...

The Yoneda lemma, according to Ravil Vakil in Foundations of Algebraic Geometry, is an "important exercise you should do once in your life." This fundamental result is often said to be difficult to conceptualize...