Subject: `wellknown'?
Date: Sun, 28 Apr 2002 17:18:52 -0400
From: jim stasheff <stasheff@email.unc.edu>
To: dondavis <dmd1@lehigh.edu>

The following was news to me and does not seem to be in the obvious
texts:

Let X --> Y be a 2-fold covering space where X and Y are n-manifolds.
 Let b_k dentoe the k-th betti number.

Claim: b_k (X) = b_k (Y) + b_{n-k} (Y)

anyone know a reference?

jim