Definition:Interval/Notation/Wirth

Definition
The notation used on this site to denote an interval of an ordered set $\left({S, \preccurlyeq}\right)$ is a fairly recent innovation, and was introduced by C.A.R. Hoare and Lyle Ramshaw:

This double dots notation has a worthy precedent in the sphere of computer languages.

For example, Pascal and Haskell use the same notation for a closed interval.