Fix typo in methods/proofs/inference-patterns.

content/methods/proofs/inference-patterns.tex

@@ -288,7 +288,7 @@ \subsection{Using Existence Claims}
 indicate this by going from ``for some $x$, $x \in A$'' to ``Let $a
 \in A$.''  Now you can reason about~$a$, use some other hypotheses, etc.,
 until you come to a conclusion, $p$. If $p$ no longer mentions~$a$, $p$ is
-independent of the asusmption that $a \in A$, and you've shown that it
+independent of the assumption that $a \in A$, and you've shown that it
 follows just from the assumption ``for some $x$, $x \in A$.''
 
 \begin{prop}