Definition:Odd-Even Topology

Definition
Let $\Z_{>0}$ denote the set of strictly positive integers:
 * $\Z_{>0} = \set {x \in \Z: x > 0}$

Let $\PP$ be the partition on $\Z_{>0}$ defined as:
 * $\PP = \set {\set {2 k - 1, 2 k}: k \in \Z_{>0} }$

That is:
 * $\PP = \set {\set {1, 2}, \set {3, 4}, \set {5, 6}, \ldots}$

Then the topology whose basis is $\PP$ is called the odd-even topology.