Open Disk

An -dimensional open disk of radius  is the collection of points of distance less than  from a fixed point in Euclidean -space. Krantz (1999, p. 3) uses the symbol  to denote the open disk, and  to denote the unit open disk centered at the origin.

The open disk for  is called an open interval, and the term open ball is often used for .

REFERENCES:

Krantz, S. G. Handbook of Complex Variables. Boston, MA: Birkhäuser, p. 3, 1999.