diff --git a/examples/derived.nelua b/examples/derived.nelua
index 35c398d..32c9a83 100755
--- a/examples/derived.nelua
+++ b/examples/derived.nelua
@@ -27,7 +27,7 @@ local io = require 'io'
 local entity = require 'rotor.entity'
 local component = require 'rotor.component'
 local derived_entity = require 'rotor.derived_entity'
-local utils = require 'rotor.utils'
+local rotor_concepts = require 'rotor.concepts'
 
 local Class = @enum{
   Person = 0,
@@ -60,14 +60,12 @@ local Person <nickname 'Person'> = @entity(record{
   person_controller: PersonController,
 })
 
-function Person.init(name: string, class: Class): Person
-  local person: Person = {
-    person_controller = {
-      =name,
-      =class
-    }
+-- the an_entity_subset_ptr accepts any entity pointer that have at least the components of Person.
+function Person.derived_init(a_person: #[rotor_concepts.value.an_entity_subset_ptr(Person.value)]#, name: string, class: Class)
+  a_person.person_controller = {
+    =name,
+    =class
   }
-  return person
 end
 
 -- warrior
@@ -80,10 +78,12 @@ local Warrior <nickname'Warrior'> = @derived_entity(Person, record{
 })
 
 function Warrior.init(name: string): Warrior
-  local person = Person.init(name, Class.Warrior)
+  local warrior: Warrior
+  Person.derived_init(&warrior, name, Class.Warrior)
 
-  local warrior = utils.copy_entity(&person, @Warrior)
-  warrior.warrior_controller.atk = 100
+  warrior.warrior_controller = {
+    atk = 100
+  }
 
   return warrior
 end
@@ -98,10 +98,12 @@ local Wizard <nickname 'Wizard'> = @derived_entity(Person, record{
 })
 
 function Wizard.init(name: string): Wizard
-  local person = Person.init(name, Class.Wizard)
-
-  local wizard = utils.copy_entity(&person, @Wizard)
-  wizard.wizard_controller.mp = 120
+  local wizard: Wizard
+  Person.derived_init(&wizard, name, Class.Warrior)
+  
+  wizard.wizard_controller = {
+    mp = 120
+  }
 
   return wizard
 end
diff --git a/examples/derived_entity_tree.nelua b/examples/derived_entity_tree.nelua
index a8e7dae..a753933 100755
--- a/examples/derived_entity_tree.nelua
+++ b/examples/derived_entity_tree.nelua
@@ -17,8 +17,7 @@ local storage   = require 'rotor.storage'
 local component = require 'rotor.component'
 local entity    = require 'rotor.entity'
 local system    = require 'rotor.system'
-local concepts  = require 'rotor.concepts'
-local utils     = require 'rotor.utils'
+local rotor_concepts  = require 'rotor.concepts'
 local derived_entity = require 'rotor.derived_entity'
 
 -- nene
@@ -82,7 +81,7 @@ local Sun.storage: storage(Sun, 1)
 local SolarSystem = @record{}
 
 -- this is a polymorphic function that accepts any pointer of an entity that have a position component
-local function position_hierarchy(entity_ptr: #[concepts.value.an_entity_ptr_with({Position.value})]#)
+local function position_hierarchy(entity_ptr: #[rotor_concepts.value.an_entity_ptr_with({Position.value})]#)
   ## local entity_type = entity_ptr.type.subtype
 
   -- for each child entity that have a position component
@@ -102,7 +101,7 @@ local function position_hierarchy(entity_ptr: #[concepts.value.an_entity_ptr_wit
   ## end
 end
 
-local function orbital_bodies_hierarchy(entity_ptr: concepts.an_entity_ptr)
+local function orbital_bodies_hierarchy(entity_ptr: rotor_concepts.an_entity_ptr)
   ## local entity_type = entity_ptr.type.subtype
   ## local pos_field = entity_type:find_field_of_type(Position.value)
 
diff --git a/examples/entity_tree.nelua b/examples/entity_tree.nelua
index 0d2d4ff..6e80443 100755
--- a/examples/entity_tree.nelua
+++ b/examples/entity_tree.nelua
@@ -17,7 +17,7 @@ local storage   = require 'rotor.storage'
 local component = require 'rotor.component'
 local entity    = require 'rotor.entity'
 local system    = require 'rotor.system'
-local concepts  = require 'rotor.concepts'
+local rotor_concepts  = require 'rotor.concepts'
 
 -- nene
 local Nene = require 'nene'
@@ -84,7 +84,7 @@ local Sun.storage: storage(Sun, 1)
 local SolarSystem = @record{}
 
 -- this is a polymorphic function that accepts any pointer of an entity that have a position component
-local function position_hierarchy(entity_ptr: #[concepts.value.an_entity_ptr_with({Position.value})]#)
+local function position_hierarchy(entity_ptr: #[rotor_concepts.value.an_entity_ptr_with({Position.value})]#)
   ## local entity_type = entity_ptr.type.subtype
 
   -- for each child entity that have a position component
@@ -104,7 +104,7 @@ local function position_hierarchy(entity_ptr: #[concepts.value.an_entity_ptr_wit
   ## end
 end
 
-local function orbital_bodies_hierarchy(entity_ptr: concepts.an_entity_ptr)
+local function orbital_bodies_hierarchy(entity_ptr: rotor_concepts.an_entity_ptr)
   ## local entity_type = entity_ptr.type.subtype
   ## local pos_field = entity_type:find_field_of_type(Position.value)
 
diff --git a/rotor/utils.nelua b/rotor/utils.nelua
index 7d1b9f1..46d5301 100755
--- a/rotor/utils.nelua
+++ b/rotor/utils.nelua
@@ -9,8 +9,6 @@ This module have some useful utility functions.
 
 -- The util module
 
-local concepts = require 'rotor.concepts'
-
 local utils = @record{}
 
 -- returns if the type it's accepted to be on an entity field.
@@ -37,35 +35,4 @@ function utils.value.assert_record_for_entity(type)
 end
 ]]
 
---[[
-Returns a value of type `new_entity_type`, whose components are copied from
-the `another_entity` argument (which must be an entity).
-
-Usage:
-```lua
--- code taken from the `derived` example
-function Warrior.init(name: string): Warrior
-  local person = Person.init(name, Class.Warrior)
-
-  local warrior = utils.copy_entity(&person, @Warrior)
-  warrior.warrior_controller.atk = 100
-
-  return warrior
-end
-```
-]]
-function utils.copy_entity(another_entity: concepts.an_entity_ptr, new_entity_type: type): #[new_entity_type.value]#
-  local new_entity: new_entity_type
-
-  ## for _, ne_field in ipairs(new_entity_type.value.fields) do
-    ## for _, ae_field in ipairs(another_entity.type.subtype.fields) do
-      ## if ne_field.type == ae_field.type then
-        new_entity.#|ne_field.name|# = another_entity.#|ae_field.name|#
-      ## end
-    ## end
-  ## end
-
-  return new_entity
-end
-
 return utils