**Defined in theory: Standard-units****Source code: standard-units.lisp**

**Documentation:**THE-NUMBER-PI is an approximation of the real number that is the ratio of the perimeter of a circle to its diameter.

**Instance-Of:**Real-number

(= The-Number-Pi 3.1415926535897936)

- Should be defined as part of kif-numbers?
**Formerly-Called:**pi- Renamed from PI because PI is a common abbreviation. In a general ontology (one that will be included and extended, it's probably a good idea to avoid short, ambiguous names.