In the discrete branches of mathematics and the computer sciences, it will only take some seconds before you're faced with a set like {1,...,m}. Some people write $1\ldotp\ldotp m$, others $\{j:1\leq j\leq m\}$, and that journal you're submitting to might want something else entirely. The 12many package provides an interface that makes changing from one to another a one-line change.

The author is Ulrich M. Schwarz. The package is Copyright © 2005 Ulrich M. Schwarz.