Added keyword c:xxx: to express that we want the concept, not its body

docs/blog.rst

@@ -767,4 +767,64 @@ Let's see an example
     def concept one as 1
     def concept two as 2
 
-    eval one + two
+    eval one + two
+
+In this situation, I expect PythonEvaluator to resolve the concepts 'one' and 'two' and to return 1 + 2, hence 3
+
+In this other situation
+
+::
+
+    def concept one as 1
+    def concept desc a as sheerka.desc(a)
+    desc one
+
+I expect Python evaluator NOT to resolve the concept one and to pass it strait to the function.
+
+Unfortunately for me, in the current implementation. 'a' is resolved to the concept 'one', which is resolved to its
+body "1". So the call failed, as there is not concept 1 (moreover, 1 is an integer, it's not even the string "1").
+
+There also be some cases where 'sheerka.desc()' expects the name of a concept (and the resolution of the concept
+will be done inside the function). In this case, it's not the body nor the concept itself that is required, but the name
+of the concept.
+
+So here are three cases where the behaviour of PythonEvaluator is required to be different. I cannot hard code theses
+behaviours as they depend on the context.
+
+The global idea, to resolve this situation is to give to Sheerka a memory. What I am currently working on is the possibility
+**to create** and **to recognize** concepts. As a recall :
+
+You can create simple concepts
+
+::
+
+    def concept one as 1
+
+or concept using bnf
+
+::
+
+    def concept twenties from bnf twenty (one | two | three...)=unit as 20 + unit
+
+
+Both can be recognised.
+But if I define
+
+::
+
+    def a plus b as a + 1
+
+
+:code:`one + two` will be recognized but twenty two plus one is not correctly implemented yet.
+
+To go back on my issue with the variables resolutions with PythonEvaluator, the idea is to implement rules that will
+recognize the concept, so you will tell Sheerka if the value, the concept or the name is expected.
+
+I am far from implementing the rules. To be honest, I don't even know now how they will look like.
+
+So I am going to introduce the keyword :code:`concept:name:` or :code:`c:name:`
+
+It will means that the concept is required.
+
+If the name is required, you can use :code:`"'name'"` or :code:`'"name"'`.
+It's already working. There is nothing to do for this one.