Corrected typo in roposal.

docs/proposal.tex

@@ -59,7 +59,7 @@ along with their expected gradations.
 \subsection{Validation and tutoring}
 
 \begin{itemize}
-    \item Validate eacg reduction step and the final input.
+    \item Validate each reduction step and the final input.
     \item If requested, select the best hint (based on the chosen strategy).
     \item Generate exercises using predefined templates.
 \end{itemize}