Evidence of absence

Evidence of absence is evidence of any kind that suggests something is missing or that it does not exist. For example:

Since it necessarily follows from the first premise that Alice will place the pie on her window-sill every time she bakes one, upon observing that there is in fact no pie on the window-sill, we can deduce that Alice did not bake a pie. This argument is called modus tollens in propositional logic, and is written in sequent notation in this manner: