Old article/thread entry in summary

[Hexis]

Hi all,

I am new with gnus.
I set it up yesterday and I can't find the answer for keeping read
articles/thred in the summary.
I found that I have to C-u before entering a group (and typing the
number of articles to fetch) but now I want to set it as default
behavior.
None of these settings seems to work in my ~/.gnus :

;;(setq gnus-summary-insert-old-articles 't)
;;(gnus-summary-insert-old-articles)
;;(setq gnus-fetch-old-headers xxxx)  (where xxx is a given number)

I would be very pleased if someone could help me.
Thanks by anticipation.

Regards,