open ball In a metric space, the set of all points whose distance δ from a fixed point a is strictly less than a specified value, the radius of the ball i.e. the set of points x for which d(x, a) < δ. The open balls form a basis for the topology.
open ball
数学辞典收录了4151条数学词条，基本涵盖了常用数学知识及数学英语单词词组的翻译及用法，是数学学习的有利工具。