diff --git a/src/robotwar/browser.clj b/src/robotwar/browser.clj
index 57de474..c5283a1 100644
--- a/src/robotwar/browser.clj
+++ b/src/robotwar/browser.clj
@@ -34,6 +34,6 @@
           (compact-shells [world]
             (update-in
               world
-              [:shells]
+              [:shells :shell-map]
               #(map (comp three-sigs-map select-shell-keys) %)))]
-    (map compact-robots worlds)))
+    (map (comp compact-shells compact-robots) worlds)))
diff --git a/src/robotwar/world.clj b/src/robotwar/world.clj
index 567a3cb..a14b752 100644
--- a/src/robotwar/world.clj
+++ b/src/robotwar/world.clj
@@ -10,6 +10,9 @@
 (defn init-world
   "initialize all the variables for a robot world."
   [programs]
+  ; TODO: have :shells and :next-shell-id be top-level fields,
+  ; and dispense with :shell-map. Need to changes stuff throughout
+  ; the project; search for shells and shell-map in clj and js.
   {:shells {:next-id 0
             :shell-map {}}
    :robots (vec (map-indexed (fn [idx program]