[v0.9.18] Introducer Nodes

Not sure I understand how to use this. To illustrate, I created a diagram for a hypothetical case:

(a) I have an existing simple cluster sharing one repo - Node 1 and Node 2. Both are trusted and I can configure them. I want to add trusted Node 3, and mesh it with Node 1 and Node 2.

(b) I want to add untrusted Node 4 and also Node 5. I do not own these nodes. I can’t edit or configure them as they are operated by other people.

© I want Node 3 to see ONLY Nodes 1 and 2. And Node 2 to ONLY see Nodes 1 and 3.

(d) I want Nodes 4 and 5 to ONLY see Node 1, and not see each other.

Pretty sure I can set this up manually, but how is this configured using the Introducer option?