evidence: On Tuesday, at North America Leaders' Summit in Mexico City, Biden said, "The four years after being vice president, I was a professor at Penn." [...] Biden once held an honorary professor position at the University of Pennsylvania (UPenn), from 2017-2021, after being vice president in Barack Obama's administration. [...] "People know I take classified documents, classified information seriously," Biden said during a press conference at the North American Leaders' Summit in Mexico City, adding, "When my lawyers were clearing out my office at the University of Pennsylvania, they set up an office for me -- when I -- the four years after being vice president, I was a professor at Penn. They found some documents in a box, in a locked cabinet, at least a closet. And as soon as they did, they realized there were several classified documents in that box."