My opinion;
Benedict is still the legal Pope.
The Pope is not allowed to resign, he must die in office. Only on his death, may another election for a new Pope occur.
So, therefore, "Pope" Benedict is an anti-Pope, and obviously, based on his actions and sayings, probably the prophesied forerunner to the anti-Christ. For example, just over Easter itself (!!!), he denied the existence of Hell. (This is intended to lead to canonical doubts by the faithful- So what was Jesus doing over the three days before He rose? Why did He lie? How can Jesus, the Son of God lie?!? etc).
I think that in previous messages, P = Pope, and the Chair is also the Pope.
‘The Chair serves the Master.’
So Pope Benedict ((Arnold)) serves Satan (his Master), and he tries to destroy the faith of as many as he can, to prepare the way for the coming of his Master (Satan, the anti-Christ).
That said, at the moment I am unsure what “P =C” in this context means.