diff --git a/src/liballoc/collections/binary_heap/mod.rs b/src/liballoc/collections/binary_heap/mod.rs
index a820a50..7168db5 100644
--- a/src/liballoc/collections/binary_heap/mod.rs
+++ b/src/liballoc/collections/binary_heap/mod.rs
@@ -845,7 +845,6 @@ impl<T: SortableByWithOrder<O>, O: TotalOrder> BinaryHeap<T, O> {
     ///
     /// assert_eq!(heap.into_sorted_vec(), [-10, 2, 4])
     /// ```
-    #[cfg(feature = "binary_heap_retain")]
     pub fn retain<F>(&mut self, mut f: F)
     where
         F: FnMut(&T) -> bool,
@@ -1479,6 +1478,20 @@ cfg_if! {
 
         impl<T> FusedIterator for IntoIter<T> {}
 
+        #[rustversion::since(1.69)]
+        impl<T> Default for IntoIter<T> {
+            /// Creates an empty `binary_heap::IntoIter`.
+            ///
+            /// ```
+            /// # use copse::binary_heap;
+            /// let iter: binary_heap::IntoIter<u8> = Default::default();
+            /// assert_eq!(iter.len(), 0);
+            /// ```
+            fn default() -> Self {
+                IntoIter { iter: Default::default() }
+            }
+        }
+
         // In addition to the SAFETY invariants of the following three unsafe traits
         // also refer to the vec::in_place_collect module documentation to get an overview
         #[cfg(feature = "inplace_iteration")]
diff --git a/src/liballoc/collections/btree/map.rs b/src/liballoc/collections/btree/map.rs
index 706a04f..ecf27b9 100644
--- a/src/liballoc/collections/btree/map.rs
+++ b/src/liballoc/collections/btree/map.rs
@@ -382,6 +382,19 @@ impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for Iter<'_, K, V> {
     }
 }
 
+impl<'a, K: 'a, V: 'a> Default for Iter<'a, K, V> {
+    /// Creates an empty `btree_map::Iter`.
+    ///
+    /// ```
+    /// # use copse::btree_map;
+    /// let iter: btree_map::Iter<'_, u8, u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
+    fn default() -> Self {
+        Iter { range: Default::default(), length: 0 }
+    }
+}
+
 /// A mutable iterator over the entries of a `BTreeMap`.
 ///
 /// This `struct` is created by the [`iter_mut`] method on [`BTreeMap`]. See its
@@ -404,6 +417,19 @@ impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for IterMut<'_, K, V> {
     }
 }
 
+impl<'a, K: 'a, V: 'a> Default for IterMut<'a, K, V> {
+    /// Creates an empty `btree_map::IterMut`.
+    ///
+    /// ```
+    /// # use copse::btree_map;
+    /// let iter: btree_map::IterMut<'_, u8, u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
+    fn default() -> Self {
+        IterMut { range: Default::default(), length: 0, _marker: PhantomData {} }
+    }
+}
+
 /// An owning iterator over the entries of a `BTreeMap`.
 ///
 /// This `struct` is created by the [`into_iter`] method on [`BTreeMap`]
@@ -433,6 +459,22 @@ impl<K: Debug, V: Debug, A: Allocator + Clone> Debug for IntoIter<K, V, A> {
     }
 }
 
+impl<K, V, A> Default for IntoIter<K, V, A>
+where
+    A: Allocator + Default + Clone,
+{
+    /// Creates an empty `btree_map::IntoIter`.
+    ///
+    /// ```
+    /// # use copse::btree_map;
+    /// let iter: btree_map::IntoIter<u8, u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
+    fn default() -> Self {
+        IntoIter { range: Default::default(), length: 0, alloc: Default::default() }
+    }
+}
+
 /// An iterator over the keys of a `BTreeMap`.
 ///
 /// This `struct` is created by the [`keys`] method on [`BTreeMap`]. See its
@@ -1861,6 +1903,19 @@ impl<K, V> Clone for Keys<'_, K, V> {
     }
 }
 
+impl<K, V> Default for Keys<'_, K, V> {
+    /// Creates an empty `btree_map::Keys`.
+    ///
+    /// ```
+    /// # use copse::btree_map;
+    /// let iter: btree_map::Keys<'_, u8, u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
+    fn default() -> Self {
+        Keys { inner: Default::default() }
+    }
+}
+
 impl<'a, K, V> Iterator for Values<'a, K, V> {
     type Item = &'a V;
 
@@ -1897,6 +1952,19 @@ impl<K, V> Clone for Values<'_, K, V> {
     }
 }
 
+impl<K, V> Default for Values<'_, K, V> {
+    /// Creates an empty `btree_map::Values`.
+    ///
+    /// ```
+    /// # use copse::btree_map;
+    /// let iter: btree_map::Values<'_, u8, u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
+    fn default() -> Self {
+        Values { inner: Default::default() }
+    }
+}
+
 decorate_if! {
     /// An iterator produced by calling `drain_filter` on BTreeMap.
     if #[cfg(feature = "btree_drain_filter")] { pub }
@@ -2025,6 +2093,19 @@ impl<'a, K, V> Iterator for Range<'a, K, V> {
     }
 }
 
+impl<K, V> Default for Range<'_, K, V> {
+    /// Creates an empty `btree_map::Range`.
+    ///
+    /// ```
+    /// # use copse::btree_map;
+    /// let iter: btree_map::Range<'_, u8, u8> = Default::default();
+    /// assert_eq!(iter.count(), 0);
+    /// ```
+    fn default() -> Self {
+        Range { inner: Default::default() }
+    }
+}
+
 impl<'a, K, V> Iterator for ValuesMut<'a, K, V> {
     type Item = &'a mut V;
 
@@ -2093,6 +2174,22 @@ impl<K, V, A: Allocator + Clone> ExactSizeIterator for IntoKeys<K, V, A> {
 
 impl<K, V, A: Allocator + Clone> FusedIterator for IntoKeys<K, V, A> {}
 
+impl<K, V, A> Default for IntoKeys<K, V, A>
+where
+    A: Allocator + Default + Clone,
+{
+    /// Creates an empty `btree_map::IntoKeys`.
+    ///
+    /// ```
+    /// # use copse::btree_map;
+    /// let iter: btree_map::IntoKeys<u8, u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
+    fn default() -> Self {
+        IntoKeys { inner: Default::default() }
+    }
+}
+
 impl<K, V, A: Allocator + Clone> Iterator for IntoValues<K, V, A> {
     type Item = V;
 
@@ -2123,6 +2220,22 @@ impl<K, V, A: Allocator + Clone> ExactSizeIterator for IntoValues<K, V, A> {
 
 impl<K, V, A: Allocator + Clone> FusedIterator for IntoValues<K, V, A> {}
 
+impl<K, V, A> Default for IntoValues<K, V, A>
+where
+    A: Allocator + Default + Clone,
+{
+    /// Creates an empty `btree_map::IntoValues`.
+    ///
+    /// ```
+    /// # use copse::btree_map;
+    /// let iter: btree_map::IntoValues<u8, u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
+    fn default() -> Self {
+        IntoValues { inner: Default::default() }
+    }
+}
+
 impl<'a, K, V> DoubleEndedIterator for Range<'a, K, V> {
     fn next_back(&mut self) -> Option<(&'a K, &'a V)> {
         self.inner.next_back_checked()
diff --git a/src/liballoc/collections/btree/mod.rs b/src/liballoc/collections/btree/mod.rs
index 7552f2f..c7d0144 100644
--- a/src/liballoc/collections/btree/mod.rs
+++ b/src/liballoc/collections/btree/mod.rs
@@ -13,7 +13,6 @@ pub mod set;
 mod set_val;
 mod split;
 
-#[doc(hidden)]
 trait Recover<Q: ?Sized> {
     type Key;
 
diff --git a/src/liballoc/collections/btree/navigate.rs b/src/liballoc/collections/btree/navigate.rs
index 7054799..3354ce2 100644
--- a/src/liballoc/collections/btree/navigate.rs
+++ b/src/liballoc/collections/btree/navigate.rs
@@ -19,6 +19,12 @@ impl<'a, K: 'a, V: 'a> Clone for LeafRange<marker::Immut<'a>, K, V> {
     }
 }
 
+impl<B, K, V> Default for LeafRange<B, K, V> {
+    fn default() -> Self {
+        LeafRange { front: None, back: None }
+    }
+}
+
 impl<BorrowType, K, V> LeafRange<BorrowType, K, V> {
     pub fn none() -> Self {
         LeafRange { front: None, back: None }
@@ -124,6 +130,12 @@ pub struct LazyLeafRange<BorrowType, K, V> {
     back: Option<LazyLeafHandle<BorrowType, K, V>>,
 }
 
+impl<B, K, V> Default for LazyLeafRange<B, K, V> {
+    fn default() -> Self {
+        LazyLeafRange { front: None, back: None }
+    }
+}
+
 impl<'a, K: 'a, V: 'a> Clone for LazyLeafRange<marker::Immut<'a>, K, V> {
     fn clone(&self) -> Self {
         LazyLeafRange { front: self.front.clone(), back: self.back.clone() }
diff --git a/src/liballoc/collections/btree/set.rs b/src/liballoc/collections/btree/set.rs
index 62851ad..0d5a782 100644
--- a/src/liballoc/collections/btree/set.rs
+++ b/src/liballoc/collections/btree/set.rs
@@ -1,6 +1,3 @@
-// This is pretty much entirely stolen from TreeSet, since BTreeMap has an identical interface
-// to TreeMap
-
 use crate::{
     default::{OrdStoredKey, OrdTotalOrder},
     SortableBy, SortableByWithOrder, TotalOrder,
@@ -21,8 +18,6 @@ use super::Recover;
 
 use crate::polyfill::*;
 
-// FIXME(conventions): implement bounded iterators
-
 /// An ordered set based on a B-Tree.
 ///
 /// See [`BTreeMap`]'s documentation for a detailed discussion of this collection's performance
@@ -1598,6 +1593,20 @@ impl<T, A: Allocator + Clone> Iterator for IntoIter<T, A> {
         self.iter.size_hint()
     }
 }
+
+impl<T> Default for Iter<'_, T> {
+    /// Creates an empty `btree_set::Iter`.
+    ///
+    /// ```
+    /// # use copse::btree_set;
+    /// let iter: btree_set::Iter<'_, u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
+    fn default() -> Self {
+        Iter { iter: Default::default() }
+    }
+}
+
 impl<T, A: Allocator + Clone> DoubleEndedIterator for IntoIter<T, A> {
     fn next_back(&mut self) -> Option<T> {
         self.iter.next_back().map(|(k, _)| k)
@@ -1611,6 +1620,22 @@ impl<T, A: Allocator + Clone> ExactSizeIterator for IntoIter<T, A> {
 
 impl<T, A: Allocator + Clone> FusedIterator for IntoIter<T, A> {}
 
+impl<T, A> Default for IntoIter<T, A>
+where
+    A: Allocator + Default + Clone,
+{
+    /// Creates an empty `btree_set::IntoIter`.
+    ///
+    /// ```
+    /// # use copse::btree_set;
+    /// let iter: btree_set::IntoIter<u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
+    fn default() -> Self {
+        IntoIter { iter: Default::default() }
+    }
+}
+
 impl<T> Clone for Range<'_, T> {
     fn clone(&self) -> Self {
         Range { iter: self.iter.clone() }
@@ -1645,6 +1670,19 @@ impl<'a, T> DoubleEndedIterator for Range<'a, T> {
 
 impl<T> FusedIterator for Range<'_, T> {}
 
+impl<T> Default for Range<'_, T> {
+    /// Creates an empty `btree_set::Range`.
+    ///
+    /// ```
+    /// # use copse::btree_set;
+    /// let iter: btree_set::Range<'_, u8> = Default::default();
+    /// assert_eq!(iter.count(), 0);
+    /// ```
+    fn default() -> Self {
+        Range { iter: Default::default() }
+    }
+}
+
 impl<T, O, A: Allocator + Clone> Clone for Difference<'_, T, O, A> {
     fn clone(&self) -> Self {
         Difference {
diff --git a/src/polyfill.rs b/src/polyfill.rs
index 6b8ad5f..edfa36d 100644
--- a/src/polyfill.rs
+++ b/src/polyfill.rs
@@ -39,7 +39,7 @@ mod definitions {
                 }
             }
 
-            #[derive(Copy, Clone, Debug)]
+            #[derive(Copy, Clone, Debug, Default)]
             pub struct Global;
 
             impl Allocator for Global {}