Set-theoretic limit

Set-theoretic limit

In mathematics, the limit of a sequence of sets "A1", "A2", ... is a set whose elements are determined by the sequence in either of two equivalent ways:
*Using indicator variables, let "xi" equal 1 if "x" is in "Ai" and 0 otherwise. If the limit as "i" goes to infinity of "xi" exists for all "x", define:lim_{i ightarrow infty} A_i = { x : lim_{i ightarrow infty} x_i = 1 }.
*Using union and intersection, define:liminf_{i ightarrow infty} A_i = igcup_i igcap_{j geq i} A_j:and:limsup_{i ightarrow infty} A_i = igcap_i igcup_{j geq i} A_j.:If these two sets are equal, then either gives the set-theoretic limit of the sequence.


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