[martyalain]

Thank you for your very detailed comment and I agree with much of what you say. Please understand that I am trying in this post to share my experience as an amateur discovering, after having manipulated quite a few "standard" languages, that many concepts can be approached as a simple text rewriting process, (forget the lambda-calculus), accessible to anyone who knows how to handle a word processor. An elementary process that only needs to be judiciously combined to build booleans, data structures and touch closely the functioning of a recursion. The post is only a skeleton that requires of course some guidance and this is what I try to do in the other linked pages. Please take the trouble to check out the site, http://lambdaway.free.fr/lambdawalks where you are welcome.