diff --git a/src/HoTTEST/Agda/Exercises/02-Exercises.lagda.md b/src/HoTTEST/Agda/Exercises/02-Exercises.lagda.md
index 1303126..6a8ffc3 100644
--- a/src/HoTTEST/Agda/Exercises/02-Exercises.lagda.md
+++ b/src/HoTTEST/Agda/Exercises/02-Exercises.lagda.md
@@ -178,5 +178,5 @@ Prove that
 
 ```agda
 decidable-equality-char : (A : Type) → has-decidable-equality A ⇔ has-bool-dec-fct A
-decidable-equality-char = ?
+decidable-equality-char = {!   !}
 ```