context: An Einstein-like Professor (representing Gonick's authorial voice) prepares to travel in his time machine to whatever place or era the chapter is about.
source: The Professor reads a passage from a historical book, which activates the time machine, a literary device.
reference_original: El profesor lee un pasaje de un libro histórico, que activa una máquina del tiempo, un instrumento literario.
reference_flipped: La profesora lee un pasaje de un libro histórico, que activa una máquina del tiempo, un instrumento literario.