diff --git a/readme.md b/readme.md
index 7524280..d69d6f8 100644
--- a/readme.md
+++ b/readme.md
@@ -442,10 +442,10 @@ compose(foo, identity) ≍ compose(identity, foo) ≍ foo
 > An object that has `extract` and `extend` functions.
 
 ```js
-let CoIdentity = v => ({
+const CoIdentity = v => ({
     val: v,
-    extract: this.v,
-    extend: f => CoIdentity(f(this))
+    extract() { return this.val },
+    extend(f) { return CoIdentity(f(this)) }
 })
 ```