In mathematics, the poset topology associated with a partially ordered set S (or poset for short) is the Alexandrov topology (open sets are upper sets) on the poset of finite chains of S, ordered by inclusion.

Let V be a set of vertices. An abstract simplicial complex Δ is a set of finite sets of vertices, known as faces $sigma\; subseteq\; V$, such that

$forall\; rho,\; sigma.\; ;\; rho\; subseteq\; sigma\; in\; Delta\; Rightarrow\; rho\; in\; Delta$

Given a simplicial complex Δ as above, we define a (point set) topology $Gamma\; subseteq\; Delta$ on Δ by letting Γ be closed if and only if Γ is a simplicial complex:

$forall\; rho,\; sigma.\; ;\; rho\; subseteq\; sigma\; in\; Gamma\; Rightarrow\; rho\; in\; Gamma$

This is the Alexandrov topology on the poset of faces of Δ.

The order complex associated with a poset, S, has the underlying set of S as vertices, and the finite chains (i.e. finite totally-ordered subsets) of S as faces. The poset topology associated with a poset S is the Alexandrov topology on the order complex associated with S.

See also

• Topological combinatorics

External links

• Poset Topology: Tools and Applications Michelle L. Wachs, lecture notes IAS/Park City Graduate Summer School in Geometric Combinatorics (July 2004)