Wednesday, 9 October 2013

general topology - Limit sequence sets

In my measure theory book I came across the following definition:
Let (An)n1 be a sequence of subsets of some set X. Define:



lim sup



\liminf_{n\to\infty} A_n:=\bigcup_{n\ge1}\bigcap_{k\ge n}A_k



Call the sequence convergent if \limsup_{n\to\infty} A_n=\liminf_{n\to\infty} A_n , in which case we define \lim_{n\to\infty} A_n:=\limsup_{n\to\infty} A_n



My question is, does this notion of convergence correspond to some sort of metric on the set of subsets of X, or is it completely unrelated to the usual concept of a limit? Thanks

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