diff --git a/src/extensions/collectible.rs b/src/extensions/collectible.rs
index 6ea67e5..25132fa 100644
--- a/src/extensions/collectible.rs
+++ b/src/extensions/collectible.rs
@@ -68,7 +68,7 @@ pub trait Collectible<Item>: IntoIterator<Item = Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![1, 2, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.delete(&2), vec![1, 2, 3]);
   ///
@@ -105,7 +105,7 @@ pub trait Collectible<Item>: IntoIterator<Item = Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![1, 2, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.delete_multi(&vec![1, 2]), vec![2, 3]);
   ///
@@ -146,14 +146,14 @@ pub trait Collectible<Item>: IntoIterator<Item = Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.combinations(0), vec![vec![]]);
   /// assert_eq!(a.combinations(1), vec![vec![1], vec![2], vec![3]]);
   /// assert_eq!(a.combinations(2), vec![vec![1, 2], vec![1, 3], vec![2, 3]]);
   /// assert_eq!(a.combinations(3), vec![vec![1, 2, 3]]);
   ///
-  /// let empty_result: Vec<Vec<i32>> = Vec::new();
+  /// let empty_result: Vec<Vec<i32>> = vec![];
   /// assert_eq!(a.combinations(4), empty_result);
   /// assert_eq!(e.combinations(2), empty_result);
   /// ```
@@ -792,7 +792,7 @@ pub trait Collectible<Item>: IntoIterator<Item = Item> {
   /// use std::collections::HashSet;
   ///
   /// let a = vec![1, 2, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// let intersection = a.intersect(&vec![4, 2, 2, 3, 4]);
   ///
@@ -910,7 +910,6 @@ pub trait Collectible<Item>: IntoIterator<Item = Item> {
     self.into_iter().map(function).collect()
   }
 
-  // FIXME -  fix the failing test case
   /// Creates a new collection containing the n largest elements of
   /// this collection in descending order.
   ///
@@ -919,10 +918,13 @@ pub trait Collectible<Item>: IntoIterator<Item = Item> {
   /// ```
   /// use cantrip::*;
   ///
-  /// let a = vec![5, 1, 3, 2, 4];
-  /// let e: Vec<i32> = Vec::new();
+  /// # let source = vec![2, 1, 3];
+  /// let a = vec![2, 1, 3];
+  /// let e: Vec<i32> = vec![];
   ///
-  /// // assert_eq!(largest(3), vec![5, 4, 3]);
+  /// assert_eq!(a.largest(2), vec![3, 2]);
+  /// # let a = source.clone();
+  /// assert_eq!(a.largest(4), vec![3, 2, 1]);
   /// assert_eq!(e.largest(3), vec![]);
   /// ```
   fn largest(self, n: usize) -> Self
@@ -933,11 +935,14 @@ pub trait Collectible<Item>: IntoIterator<Item = Item> {
     let mut iterator = self.into_iter();
     let mut heap = iterator.by_ref().map(|x| Reverse(x)).take(n).collect::<BinaryHeap<_>>();
     for item in iterator {
-      if heap.peek().unwrap().0 < item {
-        *heap.peek_mut().unwrap() = Reverse(item);
+      if let Some(mut top) = heap.peek_mut() {
+        if item > top.0 {
+          *top = Reverse(item);
+        }
       }
     }
-    heap.into_iter().rev().map(|x| x.0).collect()
+    let result: Vec<Item> = unfold(|| heap.pop()).map(|x| x.0).collect();
+    result.into_iter().rev().collect()
   }
 
   /// Creates two new collections from this collection by applying
@@ -1047,7 +1052,7 @@ pub trait Collectible<Item>: IntoIterator<Item = Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.powerset(), vec![
   ///   vec![],
@@ -1082,7 +1087,7 @@ pub trait Collectible<Item>: IntoIterator<Item = Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![2, 3, 4];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// let product = a.product();
   ///
@@ -1141,7 +1146,6 @@ pub trait Collectible<Item>: IntoIterator<Item = Item> {
     iterator.next().map(|result| iterator.fold(result, function))
   }
 
-  // FIXME -  fix the failing test case
   /// Creates a new collection containing the n smallest elements of
   /// this collection in descending order.
   ///
@@ -1150,10 +1154,13 @@ pub trait Collectible<Item>: IntoIterator<Item = Item> {
   /// ```
   /// use cantrip::*;
   ///
-  /// let a = vec![5, 1, 3, 2, 4];
-  /// let e: Vec<i32> = Vec::new();
+  /// # let source = vec![2, 3, 1];
+  /// let a = vec![2, 3, 1];
+  /// let e: Vec<i32> = vec![];
   ///
-  /// // assert_eq!(smallest(3), vec![1, 2, 3]);
+  /// assert_eq!(a.smallest(2), vec![1, 2]);
+  /// # let a = source.clone();
+  /// assert_eq!(a.smallest(4), vec![1, 2, 3]);
   /// assert_eq!(e.smallest(3), vec![]);
   /// ```
   fn smallest(self, n: usize) -> Self
@@ -1164,11 +1171,14 @@ pub trait Collectible<Item>: IntoIterator<Item = Item> {
     let mut iterator = self.into_iter();
     let mut heap = iterator.by_ref().take(n).collect::<BinaryHeap<_>>();
     for item in iterator {
-      if *heap.peek().unwrap() > item {
-        *heap.peek_mut().unwrap() = item;
+      if let Some(mut top) = heap.peek_mut() {
+        if item < *top {
+          *top = item;
+        }
       }
     }
-    heap.into_iter().collect()
+    let result: Vec<Item> = unfold(|| heap.pop()).collect();
+    result.into_iter().rev().collect()
   }
 
   /// Creates a new collection from this collection by replacing the
@@ -1183,7 +1193,7 @@ pub trait Collectible<Item>: IntoIterator<Item = Item> {
   ///
   /// # let source = vec![1, 2, 2, 3];
   /// let a = vec![1, 2, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.substitute(&2, 4), vec![1, 4, 2, 3]);
   ///
@@ -1214,7 +1224,7 @@ pub trait Collectible<Item>: IntoIterator<Item = Item> {
   ///
   /// # let source = vec![1, 2, 2, 3];
   /// let a = vec![1, 2, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.substitute_multi(&vec![2, 3], vec![4, 5]), vec![1, 4, 2, 5]);
   /// # let a = source.clone();
@@ -1268,7 +1278,7 @@ pub trait Collectible<Item>: IntoIterator<Item = Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// let sum = a.sum();
   ///
diff --git a/src/extensions/ordered.rs b/src/extensions/ordered.rs
index 8718723..45a639e 100644
--- a/src/extensions/ordered.rs
+++ b/src/extensions/ordered.rs
@@ -60,7 +60,7 @@ pub trait Ordered<Item> {
   ///
   /// let a = vec![1, 2, 2, 3];
   /// let b = vec![1, 1];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.count_unique(), 3);
   /// assert_eq!(b.count_unique(), 1);
@@ -156,7 +156,7 @@ pub trait Ordered<Item> {
   /// use cantrip::*;
   ///
   /// let a = [1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.joined(", "), "1, 2, 3");
   /// assert_eq!(e.joined(", "), "");
diff --git a/src/extensions/sequence.rs b/src/extensions/sequence.rs
index 6a5be22..eec8b7e 100644
--- a/src/extensions/sequence.rs
+++ b/src/extensions/sequence.rs
@@ -28,7 +28,7 @@ pub trait Sequence<Item> {
   ///
   /// # let source = vec![1, 2];
   /// let a = vec![1, 2];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.add_at_multi(0, vec![3, 4]), vec![3, 4, 1, 2]);
   /// # let a = source.clone();
@@ -74,7 +74,7 @@ pub trait Sequence<Item> {
   ///
   /// # let source = vec![1, 2];
   /// let a = vec![1, 2];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.add_at(0, 3), vec![3, 1, 2]);
   /// # let a = source.clone();
@@ -109,7 +109,7 @@ pub trait Sequence<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.cartesian_product(0), vec![vec![]]);
   /// assert_eq!(a.cartesian_product(1), vec![vec![1], vec![2], vec![3]]);
@@ -121,7 +121,7 @@ pub trait Sequence<Item> {
   ///   ]
   /// );
   ///
-  /// let empty_result: Vec<Vec<i32>> = Vec::new();
+  /// let empty_result: Vec<Vec<i32>> = vec![];
   /// assert_eq!(e.cartesian_product(2), empty_result);
   /// ```
   fn cartesian_product(&self, k: usize) -> Vec<Self>
@@ -184,12 +184,12 @@ pub trait Sequence<Item> {
   ///
   /// let a = vec![2, 3, 1, 1, 2, 3];
   /// let b = vec![1];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// let chunked = a.chunked_by(|&p, &n| p > 0 && n < 3);
   /// assert_eq!(chunked, vec![vec![2, 3], vec![1], vec![1], vec![2, 3]]);
   ///
-  /// let empty_result: Vec<Vec<i32>> = Vec::new();
+  /// let empty_result: Vec<Vec<i32>> = vec![];
   /// assert_eq!(b.chunked_by(|_, _| true), vec![vec![1]]);
   /// assert_eq!(e.chunked_by(|_, _| true), empty_result);
   /// ```
@@ -333,7 +333,7 @@ pub trait Sequence<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.combinations_multi(0), vec![vec![]]);
   /// assert_eq!(a.combinations_multi(1), vec![vec![1], vec![2], vec![3]]);
@@ -345,7 +345,7 @@ pub trait Sequence<Item> {
   ///   vec![1, 3, 3], vec![2, 2, 2], vec![2, 2, 3], vec![2, 3, 3], vec![3, 3, 3],
   /// ]);
   ///
-  /// let empty_result: Vec<Vec<i32>> = Vec::new();
+  /// let empty_result: Vec<Vec<i32>> = vec![];
   /// assert_eq!(e.combinations_multi(2), empty_result);
   /// ```
   fn combinations_multi(&self, k: usize) -> Vec<Self>
@@ -365,7 +365,7 @@ pub trait Sequence<Item> {
   ///
   /// # let source = vec![1, 2, 3];
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.delete_at(0), vec![2, 3]);
   /// # let a = source.clone();
@@ -397,7 +397,7 @@ pub trait Sequence<Item> {
   ///
   /// # let source = vec![1, 2, 3];
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.delete_at_multi(vec![0, 2]), vec![2]);
   /// # let a = source.clone();
@@ -564,7 +564,7 @@ pub trait Sequence<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.init(), vec![1, 2]);
   ///
@@ -1206,7 +1206,7 @@ pub trait Sequence<Item> {
   /// use crate::cantrip::*;
   ///
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.skip(2), vec![3]);
   ///
@@ -1237,7 +1237,7 @@ pub trait Sequence<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![-1, 0, 1];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.skip_while(|&x| x < 0), vec![0, 1]);
   ///
@@ -1262,7 +1262,7 @@ pub trait Sequence<Item> {
   ///
   /// # let source = vec![1, 2, 3];
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.slice(0..2), vec![1, 2]);
   /// # let a = source.clone();
@@ -1651,7 +1651,7 @@ pub trait Sequence<Item> {
   ///
   /// # let source = vec![1, 2, 3];
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.substitute_at(1, 4), vec![1, 4, 3]);
   ///
@@ -1679,7 +1679,7 @@ pub trait Sequence<Item> {
   ///
   /// # let source = vec![1, 2, 3];
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.substitute_at_multi(vec![0, 2], vec![4, 5]), vec![4, 2, 5]);
   /// # let a = source.clone();
@@ -1722,7 +1722,7 @@ pub trait Sequence<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.tail(), vec![2, 3]);
   ///
@@ -1764,7 +1764,7 @@ pub trait Sequence<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![1, 2];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.take(5), vec![1, 2]);
   ///
@@ -1793,7 +1793,7 @@ pub trait Sequence<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![-1, 0, 1];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.take_while(|&x| x <= 0), vec![-1, 0]);
   ///
@@ -1925,7 +1925,7 @@ pub trait Sequence<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.variations(0), vec![vec![]]);
   /// assert_eq!(a.variations(1), vec![vec![1], vec![2], vec![3]]);
@@ -1937,7 +1937,7 @@ pub trait Sequence<Item> {
   ///   vec![1, 2, 3], vec![1, 3, 2], vec![2, 1, 3], vec![2, 3, 1], vec![3, 1, 2], vec![3, 2, 1],
   /// ]);
   ///
-  /// let empty_result: Vec<Vec<i32>> = Vec::new();
+  /// let empty_result: Vec<Vec<i32>> = vec![];
   /// assert_eq!(e.variations(2), empty_result);
   /// ```
   fn variations(&self, k: usize) -> Vec<Self>
@@ -1969,13 +1969,13 @@ pub trait Sequence<Item> {
   ///
   /// # let source = vec![1, 2, 3, 4, 5];
   /// let a = vec![1, 2, 3, 4, 5];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.windowed(2, 1), vec![vec![1, 2], vec![2, 3], vec![3, 4], vec![4, 5]]);
   /// # let a = source.clone();
   /// assert_eq!(a.windowed(2, 2), vec![vec![1, 2], vec![3, 4]]);
   ///
-  /// let empty_result: Vec<Vec<i32>> = Vec::new();
+  /// let empty_result: Vec<Vec<i32>> = vec![];
   /// assert_eq!(e.windowed(1, 1), empty_result);
   /// ```
   fn windowed(&self, size: usize, step: usize) -> Self::This<Self>
@@ -2005,12 +2005,12 @@ pub trait Sequence<Item> {
   ///
   /// # let source = vec![1, 2, 3, 4, 5];
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.windowed_circular(2, 1), vec![vec![1, 2], vec![2, 3], vec![3, 1]]);
   /// # let a = source.clone();
   /// assert_eq!(a.windowed_circular(2, 2), vec![vec![1, 2], vec![3, 4], vec![5, 1]]);
-  /// let empty_result: Vec<Vec<i32>> = Vec::new();
+  /// let empty_result: Vec<Vec<i32>> = vec![];
   /// assert_eq!(e.windowed(1, 1), empty_result);
   /// ```
   fn windowed_circular(&self, size: usize, step: usize) -> Self::This<Self>
diff --git a/src/extensions/traversable.rs b/src/extensions/traversable.rs
index bf849f7..c023b27 100644
--- a/src/extensions/traversable.rs
+++ b/src/extensions/traversable.rs
@@ -31,7 +31,7 @@ pub trait Traversable<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert!(a.all(|&x| x > 0));
   /// assert!(e.all(|&x| x > 0));
@@ -59,7 +59,7 @@ pub trait Traversable<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert!(a.any(|&x| x > 0));
   ///
@@ -346,7 +346,7 @@ pub trait Traversable<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![-3, 0, 1, 5, -10];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.max_by(|x, y| x.cmp(y)), Some(&5));
   ///
@@ -366,7 +366,7 @@ pub trait Traversable<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![-3_i32, 0, 1, 5, -10];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.max_by_key(|x| x.abs()), Some(&-10));
   ///
@@ -398,7 +398,7 @@ pub trait Traversable<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<u32> = Vec::new();
+  /// let e: Vec<u32> = vec![];
   ///
   /// assert_eq!(a.max_of(), Some(&3));
   ///
@@ -424,7 +424,7 @@ pub trait Traversable<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![-3, 0, 1, 5, -10];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.min_by(|x, y| x.cmp(y)), Some(&-10));
   ///
@@ -444,7 +444,7 @@ pub trait Traversable<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![-3_i32, 0, 1, 5, -10];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.min_by_key(|x| x.abs()), Some(&0));
   ///
@@ -477,7 +477,7 @@ pub trait Traversable<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![1, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.min_of(), Some(&1));
   ///
@@ -504,7 +504,7 @@ pub trait Traversable<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![-3, 0, 1, 5, -10];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.minmax_by(|x, y| x.cmp(y)), Some((&-10, &5)));
   /// assert_eq!(e.minmax_by(|x, y| x.cmp(y)), None);
@@ -524,7 +524,7 @@ pub trait Traversable<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![-3_i32, 0, 1, 5, -10];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.minmax_by_key(|x| x.abs()), Some((&0, &-10)));
   /// assert_eq!(e.minmax_by_key(|x| x.abs()), None);
@@ -543,7 +543,7 @@ pub trait Traversable<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![-3_i32, 0, 1, 5, -10];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert_eq!(a.minmax_of(), Some((&-10, &5)));
   /// assert_eq!(e.minmax_of(), None);
@@ -605,7 +605,7 @@ pub trait Traversable<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![1, 2, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert!(a.subset(&vec![4, 3, 2, 2, 1]));
   /// assert!(e.subset(&vec![1]));
@@ -632,7 +632,7 @@ pub trait Traversable<Item> {
   /// use cantrip::*;
   ///
   /// let a = vec![1, 2, 2, 3];
-  /// let e: Vec<i32> = Vec::new();
+  /// let e: Vec<i32> = vec![];
   ///
   /// assert!(a.superset(&vec![3, 1]));
   /// assert!(a.superset(&vec![2, 2, 1]));