Zabrodsky's Lemma says: Suppose given a fibrant space Y and a homotopy
fiber sequence F --> E --> X with X connected. If the map Y = map(,
Y) --> map(F, Y) which is induced by F --> is a weak equivalence, th
en map(X, Y) --> map(E, Y) is a weak equivalence. This has been genera
lized by Bousfield. We improve on Bousfield's generalization and give
some applications.