General help

Ok, if I'm understanding you correctly, then maybe the thing to do is to remove the description from the section summary, put it in a label instead and restrict access to the label.

Another slightly convoluted and inelegant option is to 

• create a new empty topic with no description called "2. Conditions de vie ..." and put it directly over the 'real'  topic called "2. Conditions de vie ..."
  
• Restrict this new empty topic to students who have NOT completed section 1.
• Restrict access to the 'real' topic 2 to students who have completed section 1