I doubt that that had to be taught in the seminary.
That simple logic has and is taught in most elementary classrooms: math classrooms.
If A=B, and B=C: A=C.
Most all kids get it. But there are some who just don’t get it.
Mary is a HUMAN. Humans are sinners Mary was a sinner.
Mary was (do we have to PROVE it?) a human.
The BIBLE (which Rome assembled and compiled) says that ALL have sinned and come short of the Glory of GOD. (Do I have to PROVE it?)
Now, somehow, Rome has influenced it's minions that Mary is; somehow; NOT a sinner.
Go figger...