  In this paper we study implications of folds in both parameters of Lov\'asz'
Hom(-,-) complexes. There is an important connection between the topological
properties of these complexes and lower bounds for chromatic numbers. We give a
very short and conceptual proof of the fact that if G-v is a fold of G, then
Bd(Hom(G,H)) collapses onto Bd Hom(G-v,H), whereas Hom(H,G) collapses onto
Hom(H,G-v).
  We also give an easy inductive proof of the only nonelementary fact which we
use for our arguments: if $\phi$ is a closure operator on P, then $\Delta(P)$
collapses onto $\Delta(\phi(P))$.
