It's in the very definition of "suapte natura".

No, it isn't. It's your opinion that it refers to the pope. Kramer theology is not the same thing as Church teaching. 

No, it isn't. It's your opinion that it refers to the pope.

Please go learn what "by its very nature" means.

".....the teaching of Mystici Corporis, which says that heretics 'miserably separated themselves from the unity of the Body'; and that the exclusion from membership in the Church due to heresy takes place by the nature of heresy, i.e. suapte natura, which means directly and immediately by the nature of the act itself, and therefore neither directly, dispositively, nor in any manner 'by legitimate authority'."

Kramer, Paul. On the true and the false pope: The case against Bergoglio (p. 213). Gondolin Press. Kindle Edition.

".....the teaching of Mystici Corporis, which says that heretics 'miserably separated themselves from the unity of the Body'; and that the exclusion from membership in the Church due to heresy takes place by the nature of heresy, i.e. suapte natura, which means directly and immediately by the nature of the act itself, and therefore neither directly, dispositively, nor in any manner 'by legitimate authority'."

Kramer, Paul. On the true and the false pope: The case against Bergoglio (p. 213). Gondolin Press. Kindle Edition.

Where is the Pope mentioned in Mystici Corporis? 

Please go learn what "by its very nature" means.

Not necessary. You assume that the office of the papacy is just the same as the lay state, or priestly or bishop state, when actually the office of the papacy is above that of the lay state, or priest or bishop. Otherwise, why even have a pope? Surely, if that were the case, we only need just have synods of bishops, with no pope, like the E.O. Are you really not aware of that?

I know that the office of the papacy is the supreme office and hence unique to all other offices.  That doesn't change the fact that heresy "suapte natura" separates the heretic from the Church.

The Sacrament of Baptism "suapte natura" requires water to be valid.  Would you contradict that by saying, "Well, if the pope, who occupies the supreme Church office, uses coca cola instead, would baptize validly."?

In what way is the office of the papacy supreme, and hence unique to all other offices? That's a general question, but maybe you can answer in context of the subject at hand. 

Bye bye, Meg.  I have sufficiently proved my point.

If the office of the papacy is supreme and unique, then how is it that a formal censure by the Church isn't required for loss of office due to heresy? Even the laity are allowed a formal censure, but the office of the papacy, which is supreme, is not allowed it?

Meg, you are resisting the meaning of "suapte natura".  In your wrong interpretation, "suapte natura" does not apply to the pope in regards to the effect of the sin of public heresy.  You are resisting what is in the very definition of "suapte natura", that is, it applies in ALL cases.  Abortion is "suapte natura" evil (i.e., in ALL cases).  Likewise, the public sin of manifest formal heresy "suapte natura" separates the heretic from the Church (i.e., in ALL cases).

To be fair, St Robert Bellarmine actually didn't believe a true pope COULD fall into heresy because Christ would not allow his faith to fail.  His fifth opinion is answering the question "What if the pope could fall into heresy?"  Of course, it still begs the question.

PS.  Is Catholic Knight really Fr Kramer?