Upper Section with no Smallest Element is Open in GO-Space
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Theorem
Let $\struct {S, \preceq, \tau}$ be a generalized ordered space.
Let $U$ be an upper section in $S$ with no smallest element.
Then $U$ is open in $\struct {S, \preceq, \tau}$.
Proof
By Minimal Element in Toset is Unique and Smallest, $U$ has no minimal element.
By Upper Section with no Minimal Element:
- $U = \bigcup \set {u^\succ: u \in U}$
where $u^\succ$ is the strict upper closure of $u$.
By Open Ray is Open in GO-Space and the fact that a union of open sets is open, $U$ is open.
$\blacksquare$