[FreedomCalls]

Following this I suggest it would be prudent to find out specifically why Caerularius was excommunicated

And Cerularius excommunicated Leo IX right afterwards.

[DBeers]

And Cerularius excommunicated Leo IX right afterwards.

That would be like me attempting to excommunicate the Pope after being excommunicated -not possible EVEN if prior to my excommunication -simply because there is but one primacy/pontif.