class Concept:
 * name
 
    human reading name of the concept. It is how the concept will be referenced
 * is_builtin
    
    Simple flag to make the difference between user defined concept and builtins
    
  * is_unique
  
    To manage singleton. There should be only one instance of the concept if True
  
  * key
  
    It is the name of the concept, where all variables, or the obj are replaced by
    __var__x (x is the number of the variable). It's use to quickly find concepts
    with variables
    
  * id
  
    The key is the unique identifier for the class of concept. The concept may be
    modified along its life, but its key will never change

  * where
    
    preconditions for the variables of the concept. Body will be executed only 
    if the where conditions on the properties are True 

  * pre
    
    Execution context to verified before executing the context

  * post
    
    Post conditions to verify, once the context is executed
  
  * obj
    
    main or principal subject of the concept
  
  * body
  
    Code or value of the concept
    
   * desc
   
     explanation of the concept
    
    * digest
     
        SHA 256 of all properties. It allows 
     
    * props
    
        other properties of the concept (obj is the first one)