1.1 --- a/org/intro.org	Sat Feb 04 23:45:25 2012 -0700
     1.2 +++ b/org/intro.org	Sun Feb 05 00:02:00 2012 -0700
     1.3 @@ -125,7 +125,7 @@
     1.4  ago, and as a result it has been ported and modified for many
     1.5  different reasons. This engine was famous for its advanced use of
     1.6  realistic shading and had decent and fast physics
     1.7 -simulation. Researchers at Princeton [[http://www.nature.com/nature/journal/v461/n7266/pdf/nature08499.pdf][used this code]] to study spatial
     1.8 +simulation. Researchers at Princeton [[../sources/mouse-in-virtual-reality.pdf][used this code]] to study spatial
     1.9  information encoding in the hippocampal cells of rats. Those
    1.10  researchers created a special Quake II level that simulated a maze,
    1.11  and added an interface where a mouse could run around inside a ball in