presentation: small correction

presentation/main.tex

@@ -1240,8 +1240,8 @@ end
 \begin{frame}{Iteration: big payoff!}
   \begin{align*}
     \tt{for} :: \forall \gamma . \forall iota .&\\
-      &(\tt{item} :: \gamma \bs \tt{item}_\gamma) .\\
-      &(\tt{item} :: \iota \bs \tt{item}_\iota) .\\
+      &(\tt{item} ::_i \gamma \bs \tt{item}_\gamma) .\\
+      &(\tt{item} ::_i \iota \bs \tt{item}_\iota) .\\
       &(\tt{next} ::_i \gamma \arrow (\tt{item}_\gamma * \gamma) \tt{ option} \bs \tt{next}_\gamma) .\\
       &(\tt{insert} ::_i \iota \arrow \tt{item}_\iota \arrow \iota) .\\
       &\gamma \arrow \iota \arrow (\tt{item}_\gamma \arrow \tt{item}_\iota) \arrow \iota