fixed typo in orthogonal projection lemma

inputs/lecture_14.tex

@@ -101,7 +101,7 @@ and then do the harder proof.
     i.e.~$H$ is a vector space with an inner product $\langle \cdot, \cdot \rangle_H$ which defines a norm by $\|x\|_H^2 = \langle x, x\rangle_H$
     making $H$ a complete metric space.
 
-    For any $x \in H$ and $K \subseteq H$ closed and convex,
+    For any $x \in H$ and closed, convex subspace $K \subseteq H$,
     there exists a unique $z \in K$ such that the following equivalent conditions hold:
     \begin{enumerate}[(a)]
         \item  $\forall  y \in K : \langle x-z, y\rangle_H = 0$,