Broken link on "epstein civil violence" example #2846
Description
In the "Epstein Civil Violence" example here, under the section "Further Reading" there is a link that seems that it go to the reference paper by Joshua Epstein.
However, the current link is http://www.pnas.org/content/99/suppl.3/7243.short, which does not work.
Instead, it seems like the link should be replaced by its doi-based link, http://doi.org/10.1073/pnas.092080199.