Quick question about shared groups logic

Ok, so, I have groups 1, 2 and 3. In their shared groups section, on group 1 I have groups 2 and 3 marked, and so on. So in the end every user sees everyone else from his and other groups.

My question is, if I add group 4, for the users in it to be visible to all the other users and for them to see everyone else too, do I need to add all the other 3 groups to group 4's shared groups and then add group 4 to the other groups' shared groups or just adding the 3 first groups to the new group's will go both ways?

Thanks in advance.