Snake Lemma

An exact-sequence technique in homological algebra that, given a commutative diagram of short exact sequences, produces a long exact sequence relating kernels and cokernels (or homology groups) via a connecting homomorphism constructed by a diagram chase.

A diagram-chasing result which, from a commutative diagram of two exact rows and a column of maps, produces a canonical long exact sequence connecting kernels and cokernels, including a connecting homomorphism often denoted δ.