Thanks again laurent_R! (you are very kind too: no need to warry to disagree with me: i'm still a Discipulus (pupil))

I was underlined this point of view exactly because i wished an answer as your answer.
I think your explication is very useful for me and for future reader (i'll link it many times in the future..). I never told well the difference between recursive and itarative till your first reply. Also never noticed the difference between 'stack' and 'queue'.

I think paco too would like your explanation.

L*