A (symmetrical) boundary set of radius and center is the set of all points such that

Let be the origin. In , the boundary set is then the pair of points and . In , the boundary set is a circle. In , the boundary set is a sphere.

A (symmetrical) boundary set of radius and center is the set of all points such that

Let be the origin. In , the boundary set is then the pair of points and . In , the boundary set is a circle. In , the boundary set is a sphere.

Weisstein, Eric W. "Boundary Set." From
*MathWorld*--A Wolfram Web Resource. https://mathworld.wolfram.com/BoundarySet.html