diff --git a/src/main/java/edu/kit/typicalc/view/content/typeinferencecontent/ConstraintSetIndexFactory.java b/src/main/java/edu/kit/typicalc/view/content/typeinferencecontent/ConstraintSetIndexFactory.java
index bc2694c..ab10f09 100644
--- a/src/main/java/edu/kit/typicalc/view/content/typeinferencecontent/ConstraintSetIndexFactory.java
+++ b/src/main/java/edu/kit/typicalc/view/content/typeinferencecontent/ConstraintSetIndexFactory.java
@@ -30,8 +30,8 @@ public class ConstraintSetIndexFactory {
         String index = nextConstraintSetIndex == FIRST_CONSTRAINT_SET_INDEX
                 ? ""
                 :  nextConstraintSetIndex == FIRST_CONSTRAINT_SET_INDEX + 1
-                    ? UNDERSCORE + CURLY_LEFT + LET + CURLY_RIGHT
-                    : UNDERSCORE + CURLY_LEFT + LET + UNDERSCORE
+                    ? "" + UNDERSCORE + CURLY_LEFT + LET + CURLY_RIGHT
+                    : "" + UNDERSCORE + CURLY_LEFT + LET + UNDERSCORE
                         + CURLY_LEFT + nextConstraintSetIndex + CURLY_RIGHT + CURLY_RIGHT;
 
         nextConstraintSetIndex++;