diff -r 001fc6183d19 -r 1cfa95e6b8bb pnas/pnas.tex
--- a/pnas/pnas.tex	Mon Nov 22 19:42:06 2010 -0700
+++ b/pnas/pnas.tex	Tue Nov 23 09:28:45 2010 -0800
@@ -299,7 +299,7 @@
 Thus we can have the simplicity of strict associativity in exchange for more morphisms.
 We wish to imitate this strategy in higher categories.
 Because we are mainly interested in the case of strong duality, we replace the intervals $[0,r]$ not with
-a product of $k$ intervals (c.f. \cite{0909.2212}) but rather with any $k$-ball, that is, 
+a product of $k$ intervals (c.f. \cite{ulrike-tillmann-2008,0909.2212}) but rather with any $k$-ball, that is, 
 any $k$-manifold which is homeomorphic
 to the standard $k$-ball $B^k$.