Zen is transmitted I Shin Den Shin. ‘Shin’ is mind, or heart. So, from one real person to another. But how many is the real person? One, or many, or both?
‘Mind’ doesn’t mean the personal, karmic mind, obviously. And, likewise, heart.
In the Shiho, the document of transmission, the whole lineage is written out, one name after the other. And all the names are connected by a single red thread. A heart thread. So all the names are an expression of that heart.