Ex 4.4.1: flip tau_2 and tau_1

info/exercises/src/ex-04/ex/types.tex

@@ -103,8 +103,8 @@
       above derivation is valid.
       \item In all valid derivations, \(\tau_2 = \tau_5\).
       \item There are \emph{no} valid derivations where \(\tau_2 = \lstinline|Int|\).
-      \item In all valid derivations, \(\tau_4 = (\tau_3, \tau_5)\)
-      \item In all valid derivations, \(\tau_2 = \tau_4 \to \tau_1\)
+      \item In all valid derivations, \(\tau_4 = (\tau_3, \tau_5)\).
+      \item In all valid derivations, \(\tau_1 = \tau_4 \to \tau_2\).
       \item There is a valid derivation where \(\tau_1 = \tau_2\).
     \end{enumerate}
     \item For each of the following pairs of terms and types, provide a valid