四元数一实数和一矢量的和的表达式，有四个项，一个为实数项，另外三个为虚数项 An expression that is the sum of a real number and a vector and that contains four terms, one real and three imaginary.
闭联集与一个区间内所有实数数目相同的点的集合 A set having the same number of points as all the real numbers in an interval.
