diff --git a/lib/core_extensions/array.rb b/lib/core_extensions/array.rb
deleted file mode 100644
index 81f8aed..0000000
--- a/lib/core_extensions/array.rb
+++ /dev/null
@@ -1,19 +0,0 @@
-class Array
-  def entropy
-    each_with_object(Hash.new(0)) do |i, result|
-      result[i] += 1
-    end.values.inject(0, :+) do |count|
-      percentage = count.to_f / length
-
-      -percentage * Math.log2(percentage)
-    end
-  end
-end
-
-module ArrayClassification
-  refine Array do
-    def classification
-      collect(&:last)
-    end
-  end
-end
diff --git a/lib/core_extensions/object.rb b/lib/core_extensions/object.rb
deleted file mode 100644
index 75afe7c..0000000
--- a/lib/core_extensions/object.rb
+++ /dev/null
@@ -1,9 +0,0 @@
-class Object
-  def save_to_file(filename)
-    File.open(filename, "w+") { |f| f << Marshal.dump(self) }
-  end
-
-  def self.load_from_file(filename)
-    Marshal.load(File.read(filename))
-  end
-end
diff --git a/lib/decisiontree.rb b/lib/decisiontree.rb
index efd7a08..c862856 100644
--- a/lib/decisiontree.rb
+++ b/lib/decisiontree.rb
@@ -1,3 +1,4 @@
-require "core_extensions/object"
-require "core_extensions/array"
-require File.dirname(__FILE__) + "/decisiontree/id3_tree.rb"
+require_relative "refinements/object_persistence"
+require_relative "refinements/array_entropy"
+require_relative "refinements/array_classification"
+require_relative "decisiontree/id3_tree"
diff --git a/lib/decisiontree/id3_tree.rb b/lib/decisiontree/id3_tree.rb
index 8221962..8ce6ad6 100755
--- a/lib/decisiontree/id3_tree.rb
+++ b/lib/decisiontree/id3_tree.rb
@@ -7,6 +7,8 @@ module DecisionTree
   Node = Struct.new(:attribute, :threshold, :gain)
 
   using ArrayClassification
+  using ArrayEntropy
+  using ObjectPersistence
 
   class ID3Tree
     def initialize(attributes, data, default, type)
diff --git a/lib/refinements/array_classification.rb b/lib/refinements/array_classification.rb
new file mode 100644
index 0000000..669159d
--- /dev/null
+++ b/lib/refinements/array_classification.rb
@@ -0,0 +1,7 @@
+module ArrayClassification
+  refine Array do
+    def classification
+      collect(&:last)
+    end
+  end
+end
diff --git a/lib/refinements/array_entropy.rb b/lib/refinements/array_entropy.rb
new file mode 100644
index 0000000..3ed03b0
--- /dev/null
+++ b/lib/refinements/array_entropy.rb
@@ -0,0 +1,13 @@
+module ArrayEntropy
+  refine Array do
+    def entropy
+      each_with_object(Hash.new(0)) do |i, result|
+        result[i] += 1
+      end.values.inject(0, :+) do |count|
+        percentage = count.to_f / length
+
+        -percentage * Math.log2(percentage)
+      end
+    end
+  end
+end
diff --git a/lib/refinements/object_persistence.rb b/lib/refinements/object_persistence.rb
new file mode 100644
index 0000000..52deca3
--- /dev/null
+++ b/lib/refinements/object_persistence.rb
@@ -0,0 +1,11 @@
+module ObjectPersistence
+  refine Object do
+    def save_to_file(filename)
+      File.open(filename, "w+") { |f| f << Marshal.dump(self) }
+    end
+
+    def self.load_from_file(filename)
+      Marshal.load(File.read(filename))
+    end
+  end
+end