Snake lemma variations

Abstract

The Kernel Complex Lemma states that given commutative diagram with exact rows and exact columns which covers the region under a $\Gamma$-shape, then the kernel sequence on the top and the kernel sequence at the left have in each position isomorphic homology. The dual version, the Cokernel Complex Lemma, has been used to determine the support of a finitely presented functor on the Auslander-Reiten quiver. We note that the Snake Lemma is a consequence of the two results combined.