Fix typos in examples

Thanks to Wei Chen
https://stacks.math.columbia.edu/tag/0GIK#comment-6729

CONTRIBUTORS

@@ -65,6 +65,7 @@ Nuno Cardoso
 Scott Carnahan
 Kęstutis Česnavičius
 Antoine Chambert-Loir
+Wei Chen
 Will Chen
 William Chen
 Raymond Cheng (程毅)

examples.tex

@@ -1818,10 +1818,10 @@ \section{Taking scheme theoretic images}
 scheme theoretic image of $f$
 is not equal to the closure of the image of $f$.
 \item The formation of the scheme theoretic image does not commute
-with restriction to the open subscheme $U = \Spec(k[t. 1/t]) \subset Y$.
-Namely, the preimage of $U$ in $X$ is empty and hence the scheme theoretic
-image of $f|_{f^{-1}(U)} : f^{-1}(U) \to U$ is the empty scheme
-(and this is not equal to $X \cap U$).
+with restriction to the open subscheme $V = \Spec(k[t, 1/t]) \subset Y$.
+Namely, the preimage of $V$ in $X$ is empty and hence the scheme theoretic
+image of $f|_{f^{-1}(V)} : f^{-1}(V) \to V$ is the empty scheme.
+This is not equal to $Y \cap V$.
 \end{enumerate}