The Unit disc reference article from the English Wikipedia on 24-Apr-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Unit disc

A disc of unit radius on a plane is called a unit disc. Unless otherwise specified, the unit disc on a Cartesian plane is the unit disc about the origin, the inside of the unit circle.

A closed unit disc is the set of points whose distance from the centre is less than or equal to 1. An open unit disc is the set of points whose distance from the centre is less than 1.

See also

• open interval
• closed interval
• open set
• closed set

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