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That is one of the main, that is one of his main patristic foundations.

And by the way, you can find the Commonitorium on newadvent.org. You don't have to pay a penny.

It's available for free online.

Wanna give an incredible shout-out to the man himself.

The Great Catechism.

It is available online for free at New Advent.

There is a work called The Great Catechism from St. Gregory of Nyssa where he is very clear in teaching purgatory.

But a lot of the language is using fiery imagery.

asking for his ratification, and Pope St. Leo rejected Canon 28 while ratifying the Council's doctrinal work.

Even Anatolius of Constantinople afterwards wrote to Pope St. Leo concerning the disputed enactment, and he described it, and I'm reading directly off of Sempiternus Rex Christus on newadvent.org.

Directly from there, it says, he subsequently wrote to Pope St. Leo concerning the disputed enactment and described its validity and confirmation as reserved to Leo's authority.

Whoa! If an ecumenical council were simply above the Pope in a way that the enactments automatically bound him, then this is a pretty difficult one to explain, isn't it? No, rather the council enacted something.