On a page called 14 jokes only intellectuals will really understand, it lists:
A mathematician is heading to a house party. Just as he is coming up to the house, he notices there are no cars parked nearby, and all the lights in the house turned off.
Just then, he sees two people enter, and shortly afterwards he sees three people leave.
So he walks up and goes into the house, only to find it empty.
Now, I ain't no brainiac, but I could at least spot sources of alleged humor in the other jokes.
But this one eludes me.
The only thing obvious is the "typical word problem" construction and the fact that the house should not strictly be empty with the mathematician in it.
So what is/are the alleged punchline(s) of that joke?