Added concept 'isa' other_concept functionality

docs/blog.rst

@@ -81,8 +81,8 @@ So, you could call the concept by
 
 They will produce the strings "hello kodjo" or "hello my friend"
 
-About versioning
-""""""""""""""""
+About versionning of the information
+"""""""""""""""""""""""""""""""""""""
 As I said previously, I mimic how git_ versions its objects.
 
 ::
@@ -597,4 +597,60 @@ Like in regular expressions, you will also find
 For those who doesn't know that BNF stands for, please have a look at the bnf_
 wikipedia page.
 
-I guess that I will need a complete chapter to explain how you retrieve what was parsed
+I guess that I will need a complete chapter to explain how you retrieve what was parsed
+
+2019-12-21
+**********
+
+Implementing Inheritance
+""""""""""""""""""""""""
+
+Except that it is not inheritance, at least the way it is seen in modern programing languages.
+
+I think that I should first express what I am trying to do. I guess that it will help me
+have a better understanding myself.
+
+::
+
+    def concept one as 1
+    def concept two as 2
+    one is a number
+    two is a number
+
+When I enter :code:`one`, the result should be :code:`1`
+
+But I should be able to express other concepts by using
+
+::
+
+    def concept a plus b where a is a number and b is a number as a + b
+
+Just by reading what I have just written, we can see that 'is a' has two separate meanings.
+In the first usage, it's an affirmation, in the latter one, it's a question.
+
+Should we consider them as the same concept, with two usages, or as two separate concepts,
+which are somehow linked ?
+
+As of now, there is only one usage to all concepts, which is the property 'BODY', but I have
+prepared the property 'PRE' which can be used for that.
+
+I am a little bit making a digression. The original subject was on how I can express that a
+concept is an element of another concept. We may focus on the implementation later.
+
+So saying that 'one' is a 'number' means that there is a set called 'number'
+in which 'one' belong.
+
+The simple implementation will be to create an entry 'all_number' in sdp and to add 'one' in it.
+The two issue that I foresee are:
+
+* What about infinite sets ? (my set 'number' can never be completed if I put the item one by one)
+* What if the same name refers to different set (I don't have any example in mind, but I guess that synonyms of sets do exist)
+
+
+For the two questions, I will first try the simple implementations and see there I go from there. ie :
+
+* on the top of the entry all_numbers which lists the known numbers, you can define concepts :code:`is a number`
+  that can be also used to detect the the concept is part of the set
+* the entry in sdp will not be all_number, but all_id_of_number. I will use the concept id instead of its name
+
+