Definition:Region/Plane

Definition

A point set $R$ in the plane is a region if and only if:

$(1): \quad$ Each point of $R$ is the center of a circle all of whose elements consist of points of $R$

$(2): \quad$ Each point of $R$ can be joined by a curve consisting entirely of points of $R$.

Sources

• 2014: Christopher Clapham and James Nicholson: The Concise Oxford Dictionary of Mathematics (5th ed.) ... (previous) ... (next): Entry: region