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Specific question: Is there a name for the "topology of real lower bounds"? This is the order topology for the ordering $\supseteq$ on the set $$ \mathbb{LB} = \bigl\{ [t, \infty) \mid t \in \mathbb{R} \bigr\} \cup \bigl\{ (t, \infty) \mid t \in \mathbb{R} \bigr\}. $$ In addition to a name, is there a standard reference for its properties?

To clarify, I am not asking about a topology on $\mathbb{R}$ generated by $\mathbb{LB}$. I am asking about a topology on $\mathbb{LB}$ itself.

Motivation: I am studying a problem in operations research. The problem boils down to this: we open a box, find some amount of money $m$ inside, and have to accept or reject the money. I am specifically studying threshold policies for this problem, of which there are two types.

  • The weak threshold $t$ policy, which I'll denote ${\geq}t$, is the policy that accepts the money if and only if $m \geq t$.
  • The strict threshold $t$ policy, which I'll denote ${>}t$, is the policy that accepts the money if and only if $m > t$.

Formally, we can identify a threshold policy with the set of $m$ values it accepts, i.e. $$\begin{aligned} {\geq}t &= [t, \infty), \\ {>}t &= (t, \infty). \end{aligned}$$ So $\supseteq$ gives the "natural" ordering on threshold policies, e.g. ${\geq} 4$ is less than ${>}4$ is less than ${\geq}5$.

I'm studying a situation where I need to consider a limit of threshold policies. I cannot consider the thresholds $t$ alone, because taking a limit of policies can change the strictness of the threshold. For example, $$\begin{aligned} \lim_{\varepsilon \downarrow 0} {\geq}(t+\varepsilon) &= {>}t, \\ \lim_{\varepsilon \downarrow 0} {>}(t-\varepsilon) &= {\geq}t. \end{aligned}$$

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A slight modification of this space, where you let $t$ range over $[0,1]$ instead of $\mathbb R$, is known as the double arrow space or the split interval. You can learn more about it here or here.

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  • $\begingroup$ Perfect—thanks for the pointers! $\endgroup$
    – Ziv
    Commented Jun 24 at 7:52

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