diff --git a/lib/chapter_04.ex b/lib/chapter_04.ex
new file mode 100644
index 0000000..3c8b618
--- /dev/null
+++ b/lib/chapter_04.ex
@@ -0,0 +1,111 @@
+defmodule LittleAlchemist.Chapter04 do
+
+  def zero?(n), do: n == 0
+
+  def add1(n), do: n + 1
+  def sub1(n), do: n - 1
+
+  # def add(n, m) do
+  #   cond do
+  #     zero?(m) -> n
+  #     true -> add1(sub1(m) + n)
+  #   end
+  # end
+
+  def add(n, 0), do: n
+  def add(n, m), do: 1 + add(n, m - 1)
+
+
+  def sub(n, 0), do: n
+  def sub(n, m), do: sub(n, m - 1) - 1
+
+
+  def addtup([]), do: 0
+  def addtup([h | t]), do: add(h, addtup(t))
+
+  def addtup(t1, []), do: t1
+  def addtup([], t2), do: t2
+  def addtup([h1|t1], [h2|t2]), do: [h1 + h2 | addtup(t1, t2)]
+
+  # def addtup([], l), do: l
+  # def addtup(l, []), do: l
+  # def addtup(a, b), do: cons(add(car(a), car(b)), addtup(cdr(a), cdr(b)))
+
+  def mul(n, 1), do: n
+  def mul(n, m), do: n + mul(n, m-1)
+
+
+  def greater_than(0, _), do: false
+  def greater_than(_, 0), do: true
+  def greater_than(x, y), do: greater_than(sub1(x), sub1(y))
+
+  def less_than(_, 0), do: false
+  def less_than(0, _), do: true
+  def less_than(x, y), do: less_than(sub1(x), sub1(y))
+
+
+  # def equals(n, m) do
+  #   cond do
+  #     greater_than(n, m) -> false
+  #     less_than(n, m) -> false
+  #     true -> true
+  #   end
+  # end
+
+  def equals(0, 0), do: true
+  def equals(_, 0), do: false
+  def equals(0, _), do: false
+  def equals(n, m), do: equals(n-1, m-1)
+
+  def power(_, 0), do: 1
+  def power(n, m), do: mul(n, power(n, sub1(m)))
+
+  # def power(n, 1), do: n
+  # def power(n, m), do: n * power(n, m-1)
+
+  # def divide(n, m) do
+  #   cond do
+  #     less_than(n, m) -> 0
+  #     true -> add1(divide(sub(n, m), m))
+  #   end
+  # end
+
+  def divide(n, m) when n < m, do: 0
+  def divide(n, m), do: 1 + divide(n-m, m)
+
+  def size([]), do: 0
+  def size([_ | t]), do: 1 + size(t)
+
+  # def pick(n, lat) do
+  #   cond do
+  #     equals(sub1(n), 0) -> car(lat)
+  #     true -> pick(sub1(n), cdr(lat))
+  #   end
+  # end
+
+  def pick(1, [h | _]), do: h
+  def pick(n, [_ | t]), do: pick(n - 1, t)
+
+  def rempick(1, [_ | t]), do: t
+  def rempick(n, [h | t]), do: [h | rempick(n-1, t)]
+
+
+  def nonums([]), do: []
+  def nonums([h | t]) when is_number(h), do: nonums(t)
+  def nonums([h | t]), do: [h | nonums(t)]
+
+  def allnums([]), do: []
+  def allnums([h | t]) when not is_number(h), do: allnums(t)
+  def allnums([h | t]), do: [h | allnums(t)]
+
+  def equan(a, a), do: true
+  def equan(_, _), do: false
+
+  def occur(_, []), do: 0
+  def occur(a, [a | t]), do: 1 + occur(a, t)
+  def occur(a, [_ | t]), do: occur(a, t)
+
+  def one?(1), do: true
+  def one?(_), do: false
+
+end
diff --git a/test/chapter_04_test.exs b/test/chapter_04_test.exs
new file mode 100644
index 0000000..6f2dc68
--- /dev/null
+++ b/test/chapter_04_test.exs
@@ -0,0 +1,99 @@
+defmodule LittleAlchemist.Chapter04Test do
+  use ExUnit.Case
+  import LittleAlchemist.Chapter04
+
+  test "add1" do
+    assert add1(67) == 68
+  end
+
+  test "zero?" do
+    assert zero?(0)
+    assert zero?(42) == false
+  end
+
+  test "add" do
+    assert add(46, 12) == 58
+  end
+
+  test "sub" do
+    assert sub(14, 3) == 11
+    assert sub(17, 9) == 8
+  end
+
+  test "addtup" do
+    assert addtup([3, 5, 2, 8]) == 18
+    assert addtup([15, 6, 7, 12, 3]) == 43
+    assert addtup([3, 7], [4, 6, 8, 1]) == [7, 13, 8, 1]
+    assert addtup([3, 6, 9], [8, 5, 2, 0, 7]) == [11, 11, 11, 0, 7]
+    assert addtup([3, 7, 8], [1, 1, 1]) == [4, 8, 9]
+  end
+
+  test "mul" do
+    assert mul(5, 3) == 15
+    assert mul(13, 4) == 52
+  end
+
+  test "greater_than" do
+    refute greater_than(12, 133)
+    assert greater_than(120, 11)
+  end
+
+  test "less_than" do
+    refute less_than(4, 2)
+    assert less_than(2, 4)
+    refute less_than(0, 0)
+  end
+
+  test "equals" do
+    refute equals(2, 3)
+    assert equals(9, 9)
+  end
+
+  test "power" do
+    assert power(1, 1) == 1
+    assert power(2, 3) == 8
+    assert power(5, 3) == 125
+  end
+
+  test "divide" do
+    assert divide(5, 3) == 1
+    assert divide(7, 3) == 2
+  end
+
+  test "size" do
+    assert size([:hotdogs, :with, :mustard, :sauerkraut, :and, :pickes]) == 6
+    assert size([:ham, :and, :cheese, :on, :rye]) == 5
+  end
+
+  test "pick" do
+    assert pick(4, [:lasagna, :spaghetti, :ravioli, :macaroni, :meatball]) == :macaroni
+  end
+
+  test "rempick" do
+    assert rempick(3, [:hotdogs, :with, :hot, :mustard]) == [:hotdogs, :with, :mustard]
+  end
+
+  test "nonums" do
+    assert nonums([5, :pears, 6, :prunes, 9, :dates]) == [:pears, :prunes, :dates]
+  end
+
+  test "allnums" do
+    assert allnums([5, :pears, 6, :prunes, 9, :dates]) == [5, 6, 9]
+  end
+
+  test "equan" do
+    refute equan(:a, :b)
+    assert equan(:z, :z)
+  end
+
+  test "occur" do
+    assert occur(:c, [:a, :c, :d, :c]) == 2
+    assert occur(:c, [:z, :z, :top]) == 0
+  end
+
+  test "one" do
+    assert one?(1)
+    refute one?(9)
+  end
+
+end