diff --git a/Makefile b/Makefile
index 0558a56..402a664 100644
--- a/Makefile
+++ b/Makefile
@@ -27,7 +27,8 @@ KNOTKIT_OBJS = planar_diagram.o dt_code.o knot_diagram.o cube.o spanning_tree_co
 COMMON_OBJS = $(KNOTKIT_OBJS) $(ALGEBRA_OBJS) $(LIB_OBJS) 
 
 LIB_HEADERS = lib/lib.h lib/show.h lib/refcount.h lib/pair.h lib/maybe.h lib/vector.h \
-  lib/set.h lib/ullmanset.h lib/bitset.h lib/smallbitset.h lib/setcommon.h \
+  lib/set_wrapper.h lib/set.h lib/hashset.h \
+  lib/ullmanset.h lib/bitset.h lib/smallbitset.h lib/setcommon.h \
   lib/map_wrapper.h lib/map.h lib/hashmap.h lib/ullmanmap.h lib/mapcommon.h \
   lib/unionfind.h lib/priority_queue.h lib/io.h \
   lib/directed_multigraph.h
diff --git a/algebra/polynomial.h b/algebra/polynomial.h
index 3952544..5c3abcd 100644
--- a/algebra/polynomial.h
+++ b/algebra/polynomial.h
@@ -106,6 +106,7 @@ public:
   polynomial &operator *= (polynomial p) { return operator = (*this * p); }
   polynomial &operator *= (T s);
   
+  // ??? rename
   polynomial &add_term (T c, unsigned e)
   {
     T &c2 = coeffs[e];
diff --git a/lib/hashmap.h b/lib/hashmap.h
index 845da86..75ddae2 100644
--- a/lib/hashmap.h
+++ b/lib/hashmap.h
@@ -10,10 +10,16 @@ class hashmap : public map_wrapper<std::unordered_map<K, V, hasher<K> >, K, V>
   hashmap () { }
   hashmap (const hashmap &m) : base(m) { }
   hashmap (copy, const hashmap &m) : base(COPY, m) { }
+  hashmap (initializer_list<std::pair<const K, V> > il) : base(il) { }
   hashmap (reader &r) : base(r) { }
   ~hashmap () { }
   
   hashmap &operator = (const hashmap &m) { base::operator = (m); return *this; }
+  hashmap &operator = (initializer_list<std::pair<const K, V> > il)
+  {
+    base::operator = (il);
+    return *this;
+  }
 };
 
 template<class K, class V>
diff --git a/lib/hashset.h b/lib/hashset.h
index 2c0bc97..971eb2a 100644
--- a/lib/hashset.h
+++ b/lib/hashset.h
@@ -10,10 +10,12 @@ class hashset : public set_wrapper<std::unordered_set<T, hasher<T> >, T>
   hashset () { }
   hashset (const hashset &m) : base(m) { }
   hashset (copy, const hashset &m) : base(COPY, m) { }
+  hashset (initializer_list<T> il) : base(il) { }
   hashset (reader &r) : base(r) { }
   ~hashset () { }
   
   hashset &operator = (const hashset &m) { base::operator = (m); return *this; }
+  hashset &operator = (initializer_list<T> il) { base::operator = (il); return *this; }
 };
 
 template<class T>
diff --git a/lib/lib.h b/lib/lib.h
index 070b5e5..b507b58 100644
--- a/lib/lib.h
+++ b/lib/lib.h
@@ -10,6 +10,7 @@
 #include <gmp.h>
 #include <zlib.h>
 
+#include <initializer_list>
 #include <set>
 #include <map>
 #include <string>
@@ -167,6 +168,7 @@ using std::get;
 using std::make_tuple;
 using std::tie;
 using std::ignore;
+using std::initializer_list;
 
 #include <lib/pair.h>
 
diff --git a/lib/map.h b/lib/map.h
index 2521af3..859829a 100644
--- a/lib/map.h
+++ b/lib/map.h
@@ -11,11 +11,16 @@ class map : public map_wrapper<std::map<K, V>, K, V>
   map (unsigned dummy_size) : base(dummy_size) { }
   map (const map &m) : base(m) { }
   map (copy, const map &m) : base(COPY, m) { }
-  map (copy2, const map &m) : base(COPY2, m) { }
+  map (initializer_list<std::pair<const K, V> > il) : base(il) { }
   map (reader &r) : base(r) { }
   ~map () { }
   
   map &operator = (const map &m) { base::operator = (m); return *this; }
+  map &operator = (initializer_list<std::pair<const K, V> > il)
+  {
+    base::operator = (il);
+    return *this;
+  }
 };
 
 template<class K, class V>
diff --git a/lib/map_wrapper.h b/lib/map_wrapper.h
index 48cfacf..e263412 100644
--- a/lib/map_wrapper.h
+++ b/lib/map_wrapper.h
@@ -15,6 +15,15 @@ class map_wrapper
   {
   public:
     M t;
+    
+  public:
+    map_impl () = default;
+    map_impl (const map_impl &) = delete;
+    map_impl (const M &t_) : t(t_) { }
+    map_impl (initializer_list<std::pair<const K, V> > il) : t(il) { }
+    ~map_impl () = default;
+    
+    map_impl &operator = (const map_impl &) = delete;
   };
   
   ptr<map_impl> impl;
@@ -25,14 +34,24 @@ class map_wrapper
   
  public:
   map_wrapper () : impl(new map_impl) { }
-  map_wrapper (unsigned dummy_size) : impl(new map_impl) { }
   map_wrapper (const map_wrapper &m) : impl(m.impl) { }
-  map_wrapper (copy, const map_wrapper &m) : impl(new map_impl) { impl->t = M (m.impl->t); }
-  map_wrapper (copy2, const map_wrapper &m);
+  map_wrapper (copy, const map_wrapper &m) : impl(new map_impl (m.impl->t)) { }
+  map_wrapper (initializer_list<std::pair<const K, V> > il)
+    : impl(new map_impl (il))
+  { }
   map_wrapper (reader &r);
   ~map_wrapper () { }
   
   map_wrapper &operator = (const map_wrapper &m) { impl = m.impl; return *this; }
+  map_wrapper &operator = (initializer_list<std::pair<const K, V> > il)
+  {
+    impl->t = il;
+    return *this;
+  }
+  
+  // range-based for
+  typename M::const_iterator begin () const { return impl->t.begin (); }
+  typename M::const_iterator end () const { return impl->t.end (); }
   
   /* returns the pair associated to the smallest key */
   pair<K, V> head () const
@@ -136,15 +155,6 @@ class map_wrapper
   void write_self (writer &w) const;
 };
 
-template<class M, class K, class V>
-map_wrapper<M, K, V>::map_wrapper (copy2, const map_wrapper &m)
-  : impl(new map_impl)
-{
-  /* Keys are immutable.  Just copy the values. */
-  for (const_iter i = m; i; i ++)
-    push (i.key (), V (COPY, i.val ()));
-}
-
 template<class M, class K, class V>
 map_wrapper<M, K, V>::map_wrapper (reader &r)
   : impl(new map_impl)
diff --git a/lib/set.h b/lib/set.h
index a2aa03f..0f3e08f 100644
--- a/lib/set.h
+++ b/lib/set.h
@@ -8,13 +8,14 @@ class set : public set_wrapper<std::set<T>, T>
   
  public:
   set () { }
-  set (unsigned dummy_size) : base(dummy_size) { }
   set (const set &m) : base(m) { }
   set (copy, const set &m) : base(COPY, m) { }
+  set (initializer_list<T> il) : base(il) { }
   set (reader &r) : base(r) { }
   ~set () { }
   
   set &operator = (const set &m) { base::operator = (m); return *this; }
+  set &operator = (initializer_list<T> il) { base::operator = (il); }
   
   bool operator == (const set &s) const;
   bool operator != (const set &s) const { return !operator == (s); }
diff --git a/lib/set_wrapper.h b/lib/set_wrapper.h
index 105c6bc..a31e654 100644
--- a/lib/set_wrapper.h
+++ b/lib/set_wrapper.h
@@ -15,6 +15,15 @@ class set_wrapper
   {
   public:
     S t;
+    
+  public:
+    set_wrapper_impl () = default;
+    set_wrapper_impl (const set_wrapper_impl &) = delete;
+    set_wrapper_impl (const S &t_) : t(t_) { }
+    set_wrapper_impl (initializer_list<T> il) : t(il) { }
+    ~set_wrapper_impl () = default;
+    
+    set_wrapper_impl &operator = (const set_wrapper_impl &) = delete;
   };
   
   ptr<set_wrapper_impl> impl;
@@ -25,13 +34,25 @@ class set_wrapper
   
  public:
   set_wrapper () : impl(new set_wrapper_impl) { }
-  set_wrapper (unsigned dummy_size) : impl(new set_wrapper_impl) { }
   set_wrapper (const set_wrapper &s) : impl(s.impl) { }
-  set_wrapper (copy, const set_wrapper &s) : impl(new set_wrapper_impl) { impl->t = S (s.impl->t); }
+  set_wrapper (copy, const set_wrapper &s)
+    : impl(new set_wrapper_impl (s.impl->t))
+  { }
+  set_wrapper (initializer_list<T> il)
+    : impl(new set_wrapper_impl (il))
+  { }
   set_wrapper (reader &r);
   ~set_wrapper () { }
   
   set_wrapper &operator = (const set_wrapper &s) { impl = s.impl; return *this; }
+  set_wrapper &operator = (initializer_list<T> li)
+  {
+    impl->t = li;
+  }
+  
+  // range-based for
+  typename S::const_iterator begin () const { return impl->t.begin (); }
+  typename S::const_iterator end () const { return impl->t.end (); }
   
   T pop ()
   {
diff --git a/lib/ullmanset.h b/lib/ullmanset.h
index 658fc33..d6599ad 100644
--- a/lib/ullmanset.h
+++ b/lib/ullmanset.h
@@ -2,12 +2,15 @@
 template<unsigned B> class ullmanset_iter;
 template<unsigned B> class ullmanset_const_iter;
 
+template<unsigned B> class ullmanset_const_stl_iter;
+
 template<unsigned B>
 class ullmanset
 {
  private:
   friend class ullmanset_iter<B>;
   friend class ullmanset_const_iter<B>;
+  friend class ullmanset_const_stl_iter<B>;
   
   class keypos
   {
@@ -16,57 +19,56 @@ class ullmanset
     unsigned pos;
   };
   
-  class data
+  class data : public refcounted
   {
   public:
-    unsigned refcount;
     unsigned size;
     unsigned n;
     keypos kp[1];
+    
+  public:
+    inline void delete_at_pos (unsigned p);
   };
   
-  data *d;
-  
-  void ref (data *newd) { assert (!d); d = newd; if (d) d->refcount ++; }
-  void unref ();
-  
-  inline void delete_at_pos (unsigned p);
+  ptr<data> d;
   
  public:
   typedef ullmanset_iter<B> iter;
   typedef ullmanset_const_iter<B> const_iter;
   
  public:
-  ullmanset () : d(0) { }
   ullmanset (unsigned size);
-  ullmanset (const ullmanset &s) : d(0) { ref (s.d); }
+  ullmanset () : ullmanset(0) { }
+  ullmanset (const ullmanset &s) : d(s.d) { }
   ullmanset (copy, const ullmanset &s);
-  // ullmanset (const unsignedset &t);
   ullmanset (const bitset &t);
+  ullmanset (unsigned size, initializer_list<unsigned> il);
   ullmanset (reader &r);
-  ~ullmanset () { unref (); }
+  ~ullmanset () { }
   
-  ullmanset &operator = (const ullmanset &s) { unref (); ref (s.d); return *this; }
-  // ullmanset &operator = (const unsignedset &t);
+  ullmanset &operator = (const ullmanset &s) { d = s.d; return *this; }
   ullmanset &operator = (const bitset &t);
   
-  unsigned size () const { return d ? d->size : 0; }
+  // range-based for
+  inline ullmanset_const_stl_iter<B> begin () const;
+  inline ullmanset_const_stl_iter<B> end () const;
   
-  bool is_empty () const { assert (d); return d->n == 0; }
-  unsigned card () const { assert (d); return d->n; }
-  unsigned head () const { assert (d); assert (d->n > 0); return d->kp[0].key; }
+  unsigned size () const { return d->size; }
+  
+  bool is_empty () const { return d->n == 0; }
+  unsigned card () const { return d->n; }
+  unsigned head () const { assert (d->n > 0); return d->kp[0].key; }
   
   bool operator == (const ullmanset &s);
   bool operator != (const ullmanset &s) { return !operator == (s); }
   
   void restore (unsigned old_card)
   {
-    assert (d);
     assert (d->n >= old_card);
     d->n = old_card;
   }
   
-  void clear () { if (d) { d->n = 0; } }
+  void clear () { d->n = 0; }
   
   inline void push (unsigned k);
   inline void operator += (unsigned k); // ??? should these be inline?
@@ -88,89 +90,75 @@ class ullmanset
   
   bool operator % (unsigned k) const
   {
-    assert (d);
     assert ((k - B) >= 0);
     assert ((k - B) < d->size);
     unsigned p = d->kp[k - B].pos;
     return p < d->n && d->kp[p].key == k;
   }
+  
   bool operator () (unsigned k) const { return operator % (k); }
   
   // always 0-based
-  unsigned nth (unsigned p) const { assert (d); assert (p < d->n); return d->kp[p].key; }
+  unsigned nth (unsigned p) const
+  {
+    assert (p < d->n);
+    return d->kp[p].key;
+  }
   
-  unsigned position (unsigned k) const { assert (operator % (k)); return d->kp[k - B].pos; }
+  unsigned position (unsigned k) const
+  {
+    assert (operator % (k));
+    return d->kp[k - B].pos;
+  }
   
   void write_self (writer &w) const;
 };
 
 template<unsigned B> void
-ullmanset<B>::unref ()
+ullmanset<B>::data::delete_at_pos (unsigned p)
 {
-  if (d && --d->refcount == 0)
-    {
-      delete [] (char *)d;
-      d = 0;
-    }
-}
-
-template<unsigned B> void
-ullmanset<B>::delete_at_pos (unsigned p)
-{
-  assert (d);
-  assert (p < d->n);
-  unsigned n = --d->n;
+  assert (p < n);
+  --n;
   if (p != n)
     {
-      unsigned ell = d->kp[n].key;
-      d->kp[ell - B].pos = p;
-      d->kp[p].key = ell;
+      unsigned ell = kp[n].key;
+      kp[ell - B].pos = p;
+      kp[p].key = ell;
     }
 }
 
 template<unsigned B>
 ullmanset<B>::ullmanset (unsigned size)
-  : d(0)
 {
   data *newd = (data *)new char[sizeof (data)
 				+ sizeof (keypos) * size
 				- sizeof (keypos)];
-  newd->refcount = 0;
+  new (newd) data;
   newd->size = size;
   newd->n = 0;
-  ref (newd);
+  d = newd;
+}
+
+template<unsigned B>
+ullmanset<B>::ullmanset (unsigned size, initializer_list<unsigned> il)
+  : ullmanset(size)
+{
+  for (unsigned i : il)
+    operator += (i);
 }
 
 template<unsigned B>
 ullmanset<B>::ullmanset (copy, const ullmanset &s)
-  : d(0)
+  : ullmanset(s.size ())
 {
-  if (s.d)
-    {
-      unsigned bytes = (sizeof (data)
-			+ sizeof (keypos) * s.d->size
-			- sizeof (keypos));
-      data *newd = (data *)new char[bytes];
-      memcpy (newd, s.d, bytes);
-      newd->refcount = 0;
-      ref (newd);
-    }
+  d->n = s.d->n;
+  memcpy (&d->kp[0], &s.d->kp[0], sizeof (keypos) * d->n);
 }
 
 template<unsigned B>
 ullmanset<B>::ullmanset (reader &r)
-  : d(0)
+  : ullmanset(r.read_unsigned ())
 {
-  unsigned size_ = r.read_unsigned ();
-  if (size_ > 0)
-    {
-      data *newd = (data *)new char[sizeof (data) + sizeof (keypos) * (size_ - 1)];
-      newd->refcount = 0;
-      newd->size = size_;
-      newd->n = 0;
-      ref (newd);
-    }
-  
   unsigned card_ = r.read_unsigned ();
   for (unsigned i = 0; i < card_; i ++)
     push (r.read_unsigned ());
@@ -179,8 +167,6 @@ ullmanset<B>::ullmanset (reader &r)
 template<unsigned B> bool
 ullmanset<B>::operator == (const ullmanset &s)
 {
-  assert (d);
-  assert (s.d);
   if (d->n != s.d->n)
     return 0;
   for (iter i = *this; i; i ++)
@@ -194,7 +180,6 @@ ullmanset<B>::operator == (const ullmanset &s)
 template<unsigned B> void
 ullmanset<B>::push (unsigned k)
 {
-  assert (d);
   assert (!operator % (k));
   unsigned p = d->n ++;
   d->kp[p].key = k;
@@ -204,7 +189,6 @@ ullmanset<B>::push (unsigned k)
 template<unsigned B> void
 ullmanset<B>::operator += (unsigned k)
 {
-  assert (d);
   assert ((k - B) >= 0);
   assert ((k - B) < d->size);
   if (!operator % (k))
@@ -218,13 +202,12 @@ ullmanset<B>::operator += (unsigned k)
 template<unsigned B> void
 ullmanset<B>::operator -= (unsigned k)
 {
-  assert (d);
   assert ((k - B) >= 0);
   assert ((k - B) < d->size);
   if (operator % (k))
     {
       unsigned p = d->kp[k - B].pos;
-      delete_at_pos (p);
+      d->delete_at_pos (p);
     }
 }
   
@@ -270,22 +253,49 @@ ullmanset<B>::write_self (writer &w) const
     write (w, i.val ());
 }
 
+template<unsigned B>
+class ullmanset_const_stl_iter
+{
+ private:
+  ptr<typename ullmanset<B>::data> d;
+  unsigned p;
+  
+ public:
+  ullmanset_const_stl_iter (const ullmanset<B> &s, unsigned p_) : d(s.d), p(p_) { }
+  
+  bool operator != (const ullmanset_const_stl_iter &end) const { return p != end.p; }
+  unsigned operator * () const { assert (p < d->n); return d->kp[p].key; }
+  ullmanset_const_stl_iter &operator ++ () { p ++; return *this; }
+};
+
+template<unsigned B> ullmanset_const_stl_iter<B>
+ullmanset<B>::begin () const
+{
+  return ullmanset_const_stl_iter<B> (*this, 0);
+}
+
+template<unsigned B> ullmanset_const_stl_iter<B>
+ullmanset<B>::end () const
+{
+  return ullmanset_const_stl_iter<B> (*this, d->n);
+}
+
 template<unsigned B>
 class ullmanset_iter
 {
  private:
-  ullmanset<B> &s;
+  ptr<typename ullmanset<B>::data> d;
   unsigned i;
   bool deleted;
   
  public:
-  ullmanset_iter (ullmanset<B> &s_) : s(s_), i(0), deleted(0) { assert (s_.d); }
+  ullmanset_iter (ullmanset<B> &s) : d(s.d), i(0), deleted(0) { }
   ~ullmanset_iter () { }
   
-  void del () { assert (!deleted); assert (i < s.d->n); s.delete_at_pos (i); }
-  unsigned val () const { assert (!deleted); assert (i < s.d->n); return s.d->kp[i].key; }
-  unsigned pos () const { assert (!deleted); assert (i < s.d->n); return i; }
-  operator bool () const { assert (!deleted); return i < s.d->n; }
+  void del () { assert (!deleted); assert (i < d->n); d->delete_at_pos (i); }
+  unsigned val () const { assert (!deleted); assert (i < d->n); return d->kp[i].key; }
+  unsigned pos () const { assert (!deleted); assert (i < d->n); return i; }
+  operator bool () const { assert (!deleted); return i < d->n; }
   void operator ++ () { if (deleted) deleted = 0; else i ++; }
   void operator ++ (int) { operator ++ (); }
 };
@@ -294,16 +304,16 @@ template<unsigned B>
 class ullmanset_const_iter
 {
  private:
-  const ullmanset<B> &s;
+  ptr<typename ullmanset<B>::data> d;
   unsigned i;
   
  public:
-  ullmanset_const_iter (const ullmanset<B> &s_) : s(s_), i(0) { assert (s_.d); }
+  ullmanset_const_iter (const ullmanset<B> &s) : d(s.d), i(0) { }
   ~ullmanset_const_iter () { }
   
-  unsigned val () const { assert (i < s.d->n); return s.d->kp[i].key; }
-  unsigned pos () const { assert (i < s.d->n); return i; }
-  operator bool () const { return i < s.d->n; }
+  unsigned val () const { assert (i < d->n); return d->kp[i].key; }
+  unsigned pos () const { assert (i < d->n); return i; }
+  operator bool () const { return i < d->n; }
   void operator ++ () { i ++; }
   void operator ++ (int) { i ++; }
 };
diff --git a/main.cpp b/main.cpp
index 2ae5f6e..9ba848a 100644
--- a/main.cpp
+++ b/main.cpp
@@ -127,6 +127,47 @@ rank_lte (multivariate_laurentpoly<Z> p,
 int
 main ()
 {
+#if 0
+  ullmanset<1> empty;
+  assert (empty.size () == 0);
+  assert (empty.card () == 0);
+  assert (empty.is_empty ());
+  
+  ullmanset<1> empty2;
+  assert (empty == empty2);
+
+  ullmanset<1> emptycopy (COPY, empty);
+  assert (emptycopy == empty);
+  
+  ullmanset<1> s (50, {1,2,5,5,2,1,3,4});
+  assert (s.card () == 5);
+  
+  ullmanset<1> scopy (COPY, s);
+  assert (scopy == s);
+  
+  printf ("s:");
+  for (int x : s)
+    printf (" %d", x);
+  newline ();
+#endif
+  
+  map<unsigned, const char *> m = { { 5, "foo" }, { 11, "bar" } };
+  
+  hashmap<unsigned, const char *> m2 = { { 5, "foo" }, { 11, "bar" }, { 37, "baz" } };
+  for (std::pair<unsigned, const char *> i : m2)
+    {
+      printf ("%d -> %s\n", i.first, i.second);
+    }
+  
+#if 0
+  set<unsigned> s {1,2,5,5,2,1,3,4};
+  printf ("s:");
+  for (int x : s)
+    printf (" %d", x);
+  newline ();
+#endif
+  
+#if 0
   basedvector<int, 1> v (4);
   v[1] = 2;
   v[2] = -1;
@@ -205,6 +246,7 @@ main ()
     assert (sleb == sleb2);
     assert (uleb == uleb2);
   }
+#endif
   
 #if 0