  We prove that any smooth Riemannian manifold of non-negative scalar curvature
and with a strictly mean convex and compact boundary component can be (C^2)
extended beyond the component to have non-negative scalar curvature and to
enjoy anyone of the following three types of (new) boundary: strictly convex,
totally geodesic or strictly concave. The extension procedure can be applied
for instance to "positive mass" type of theorems.
