diff --git a/resources/koans.clj b/resources/koans.clj
index 6f35a56..89c155e 100644
--- a/resources/koans.clj
+++ b/resources/koans.clj
@@ -216,7 +216,7 @@
                            {:last-name "Smith" :id 1}]
                         2 [{:name "Mike" :id 2}]}
                        nil
-                       {:nauty-list [{:name "Jimmy" :bad true}
-                                     {:name "Joe" :bad true}]
+                       {:naughty-list [{:name "Jimmy" :bad true}
+                                       {:name "Joe" :bad true}]
                         :nice-list [{:name "Jack" :bad false}]}]}]
 ]
diff --git a/src/koans/21_group_by.clj b/src/koans/21_group_by.clj
index 245a95a..bd926fc 100644
--- a/src/koans/21_group_by.clj
+++ b/src/koans/21_group_by.clj
@@ -4,29 +4,32 @@
 
 (meditations
 
-  "To split a collection categorized by keys use the group-by function."
+  "To categorize a collection by some function, use group-by."
   (= __ (group-by count ["hello" "world" "foo" "bar"]))
 
 
-  "Sometimes you want to filter a sequence but also keep the predicate."
-  (= (get-odds-and-evens '(1 2 3 4 5))
-    [[1 3 5] [2 4]])
+  "You can simulate filter + remove in one pass"
+  (= (get-odds-and-evens [1 2 3 4 5])
+     ((partial (juxt filter remove) odd?) [1 2 3 4 5])
+     [[1 3 5] [2 4]])
 
   "You can also group by a primary key"
   (= __
      (group-by :id [{:id 1 :name "Bob"}
-                   {:id 2 :name "Mike"}
-                   {:id 1 :last-name "Smith"} ]))
+                    {:id 2 :name "Mike"}
+                    {:id 1 :last-name "Smith"} ]))
 
-  "but be careful when you group by non primary key"
-  (= {"Bob" [{:name "Bob" :id 1}], "Mike" [{:name "Mike" :id 2}], __ [{:last-name "Smith" :id 1}]}
+  "But be careful when you group by non-required key"
+  (= {"Bob" [{:name "Bob" :id 1}]
+      "Mike" [{:name "Mike" :id 2}]
+      __ [{:last-name "Smith" :id 1}]}
    (group-by :name [{:id 1 :name "Bob"}
                     {:id 2 :name "Mike"}
                     {:id 1 :last-name "Smith"}]))
 
-  "The true power of group-by is using a custom function"
+  "The true power of group-by comes with custom functions"
   (= __
-     (group-by #(if (:bad %) :nauty-list :nice-list)
+     (group-by #(if (:bad %) :naughty-list :nice-list)
                [{:name "Jimmy" :bad true}
                 {:name "Jack" :bad false}
                 {:name "Joe" :bad true}])))