Conversation so far:
Who is Sigmund Freud's friend Wilhelm Fliess?
During this formative period of his work, Sigmund Freud valued on the intellectual and emotional support of his friend Wilhelm Fliess, a Berlin-based ear, nose and throat specialist.
What was Sigmund Freud and Wilhelm Fliess' relationship?
Sigmund Freud and Wilhelm Fliess saw themselves as isolated from the prevailing clinical and theoretical mainstream because of their ambitions to develop radical new theories of sexuality.

Question: Did they collaborate?
Self-contained rewrite: Did Sigmund Freud and Wilhelm Fliess collaborate?