Individual Perception

Are people other than Fiorella real?  Or is everyone else a Golem, a simulacrum, a souless stage prop? After all, if everyone else is also real, why is it that Fiorella knows only what she is thinking and not what anyone else is?  

Maybe Fiorella is all alone in the universe and everyone else in a product of her ever-fertile imagination. Or maybe the whole universe is.