  An exact solution of the vacuum Einstein field equations over a
nonsimply-connected manifold is presented. This solution is spherically
symmetric and has no curvature singularity. It can be considered to be a
regularization of the Schwarzschild solution over a simply-connected manifold,
which has a curvature singularity at the center. Spherically symmetric collapse
of matter in R^4 may result in this nonsingular black-hole solution, if
quantum-gravity effects allow for topology change near the center.
