diff --git a/src/HottBook/Chapter2.lagda.md b/src/HottBook/Chapter2.lagda.md
index 1681b5b..2c2d9cf 100644
--- a/src/HottBook/Chapter2.lagda.md
+++ b/src/HottBook/Chapter2.lagda.md
@@ -397,8 +397,10 @@ theorem2∙13∙1 m n = encode m n , equiv
       let
         what = encode zero zero refl
         what2 = decode zero zero c
-        third = theorem2∙8∙1 what c
-      in {!   !}
+        what3 = theorem2∙8∙1 what c
+        what4 = isequiv.g (Σ.snd what3)
+        what5 = what4 tt
+      in what5
     backward (suc m) (suc n) c = {!   !}
 
     equiv = record