In the treaty of modern schism Saint Vincent Ferrer explains:
Sixth. It is true of faith that the pope has full power over all; Therefore Christ said to Peter, "whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven.” (Matt. XVI, 19). If there were two popes at the same time, or the one would have more power than the other, or not. If one had no more power than the other, neither of them would be pope, because the pope has power over all, as has been said. If he had it, the inferior would not be pope".