柯西序列
If formula_67 is a uniformly continuous map between the metric spaces "M" and "N" and ("x""n") is a Cauchy sequence in "M", then formula_68 is a Cauchy sequence in "N". If formula_69 and formula_70 are two Cauchy sequences in the rational, real or complex numbers, then the sum formula_71 and the product formula_72 are also Cauchy sequences.