Ouroboros multicast conjecture

The Ouroboros multicast conjecture (apologies, but we had to give it some name) states that it's not possible to make unicast or multicast/broadcast transparent to the entity that directly engages in the unicast or multicast communication. Or similarly, it is not possible to engage in multicast and unicast with the same API. We are still looking for a more adequate formal description of this (seemingly trivial) conjecture.