  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.
