fix wordo

svn:r3604

doc/design-paper/challenges.tex

@@ -186,7 +186,7 @@ their popular Java Anon Proxy anonymizing client.
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 \noindent
 {\bf Threat models and design philosophy.}
-The ideal Tor network would be practical, useful and and anonymous. When
+The ideal Tor network would be practical, useful and anonymous. When
 trade-offs arise between these properties, Tor's research strategy has been
 to remain useful enough to attract many users,
 and practical enough to support them.  Only subject to these