Concept
Existence proof
2 essays name this object, across one field. What follows is each of them, and the objects they name alongside it.
Also named here as pigeonhole principle — the same set of essays touches all of them, so they are one junction rather than several.
More things than boxes
If there are more objects than containers, some container holds two. That is the entire principle, it is impossible to disagree with, and it settles questions that look nothing like it.
Six people at a party
Among any six people, three are mutual acquaintances or three are mutual strangers. Five is not enough, and the arrangement that saves five is a pentagon. Beyond that the numbers become unknowable.
Named alongside it
The objects these essays reach for when they reach for this one.
Counting argumentNonconstructivePigeonhole principleComplete graphDirichletGraphParityProbabilistic methodRamsey number