In voting system

Voting system

A voting system or electoral system is a method by which voters make a choice between options, often in an election or on a policy referendum....

s, the Landau set (or uncovered set, or Fishburn set) is the set of candidates x such that for every other candidate y, there is some candidate z (possibly the same as x, but distinct from y) such that y is not preferred to x and z is not preferred to y.

The Landau set is a nonempty subset of the Smith set

Smith set

In voting systems, the Smith set, named after John H. Smith, is the smallest non-empty set of candidates in a particular election such that each member beats every other candidate outside the set in a pairwise election. The Smith set provides one standard of optimal choice for an election outcome...

. It was discovered by Nicholas Miller.