Definition:Enumeration/Notation

Notation for Enumeration
In order to avoid tedious case distinctions between finite and countably infinite sets, many authors write:


 * Let $X = \set {x_1, x_2, \ldots}$ [...]

implying that $X$ be countable, but not excluding the possibility that $X$ is actually finite.

Some authors use the abbreviated notation $\set {x_1}$ for both.