Nemo agens in causa sua
A Latinism I made up in December 2022, based on the more famous nemo iudex in causa sua: “one cannot be one’s own agent”. The bleeding obvious, you would think, but you would be surprised how resourceful structurers hit upon interposing a ghostlike agency arrangement between to desks or divisions of the same legal entity to get around some accouting or regulatory inconvenience.
An agent which represents itself has got a special name in legal parlance: a “principal”.