Yea, grip the remnant of the seatpost in a bench vise, and twist the frame Off of it.



Recent update, I observed, a friend's Peugeot, badly corroded,
the post would not Budge But the brazing attaching of the seat stay tops would give way, first..

So the paint is going anyhow to both heat the steel to re braze
as well as try to break the seized post loose..

People: grease those aluminum posts in steel frames , take it out and redo it occasionally ..