- (mathematics, somewhat informal) Proof in stages, each of which, in general, depends on the previous stages and can be visualized by means of a diagram of morphisms.
- 2016, Emily Riehl, Category Theory in Context (Aurora: Dover modern math originals), New York: Dover, →ISBN, OCLC 976394474, page x:
- Category theory also contributes new proof techniques, such as diagram chasing or arguments by duality; Steenrod called these methods “abstract nonsense.”3 The aim of this text is to introduce the language, philosophy, and basic theorems of category theory. A complementary objective is to put this theory into practice: studying functoriality in algebraic topology, naturality in group theory, and universal properties in algebra.
- To prove the five lemma, just use diagram chasing.