However, I just cannot understand what happens in slide 2. Two R_F resistances appears: but why? I thought of Miller theorem, but the Z1,Z2 values aren't close to the original 100kOhm value. Could you explain me what is the circuit transformation?
EDIT: Just to clarify: this is how I'd draw the schematic in slide 2. Apparently it isn't equivalent to the one in the slides. Why Rf is being doubled and grounded? I don't fully understand the explanation "it needs to be considered both in input and output parts".