柯西序列
A Cauchy sequence ("y"1, "y"2, …) in "Y" can be identified with a Cauchy-continuous function from {1, 1/2, 1/3, …} to "Y", defined by "f"(1/"n") = "y""n". If "Y" is complete, then this can be extended to {1, 1/2, 1/3, …, 0}; "f"(0) will be the limit of the Cauchy sequence.