I understand now that an array can contain only scalars and not other arrays.It may seem trivial for fine monks that you are, but it was not for me.
In fact, I think that my need is for an array of arrays as explained in perllol.
I always develop with "warnings" and "strict", and my syntax were correct here, even if it were a nonsense. The problem is that I do not use perl regularly enough, so I forget... Tnak you again.