Copyright © 2010 Alfonso Romero and Rafael M. Rubio. This is an open access article distributed under the
Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
A characterization for the entire solutions of a nonlinear inequality, which has a natural
interpretation in terms of certain nonflat Robertson-Walker spacetimes, is given. As an
application, new Calabi-Bernstein type problems are solved.