@@ -2,7 +2,7 @@
 extern crate void;

 use std::cmp::Ordering;
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 use std::hash::Hash;

 mod eval;
@@ -30,7 +30,7 @@
 }

 /// Convenience type, maps an instance of a type to an Arc containing a clone of the instance.
-type SelfMap<T> = HashMap<T, Container<T>>;
+type SelfMap<T> = HashSet<Container<T>>;

 /// A struct that contains canonicalization maps for every node type, as well as maps to
 /// memoize partial derivatives.
@@ -379,12 +379,11 @@
     fn insert(&self, env: &mut Environment<T>) -> Container<Self>
         where Self: Sized + Clone + Eq + Hash
     {
-        if !self.get_storage(env).contains_key(self) {
+        if !self.get_storage(env).contains(self) {
             let key = self.fancy_clone(env);
-            let value = key.clone();
-            self.get_storage(env).insert(key, container(value));
+            self.get_storage(env).insert(container(key));
         }
-        self.get_storage(env)[self].clone()
+        self.get_storage(env).get(self).unwrap().clone()
     }
 }