Infinitely often and almost always: Difference between revisions
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<math>\inf_{N \geq 1} \sup_{n \geq N} |a_n - x| \leq \epsilon</math> | <math>\inf_{N \geq 1} \sup_{n \geq N} |a_n - x| \leq \epsilon</math> | ||
<math>\sup_{N \geq 1} \inf_{n \geq N} |a_n - x| \leq \epsilon</math> | <math>\sup_{N \geq 1} \inf_{n \geq N} |a_n - x| \leq \epsilon</math> -- I think this one is equivalent to infinitely often, which is confusing since now the quantifier order has seemingly switched. | ||
[[Category:Probability]] | [[Category:Probability]] | ||
Revision as of 22:10, 31 July 2019
Let be a sequence of events in some sample space . Let be an outcome.
In the following table, all statements in the "infinitely often" column are logically equivalent. Similarly, all statements in the "almost always" column are logically equivalent.
| perspective | infinitely often | almost always |
|---|---|---|
| unions and intersections | ||
| first-order quantifiers | ||
| verbal expression | for infinitely many | for almost all , i.e. for all but finitely many , i.e. for finitely many |
| lim sup/lim inf | ||
| limit of sup/inf |
Analogy with sequences of real numbers
Let be a sequence of real numbers, let be a real number, and let be a real number.
We say is eventually -close to iff there exists some such that for all we have .
We say that is continually -adherent iff for every there exists some such that .
I think we can even define .
-- I think this one is equivalent to infinitely often, which is confusing since now the quantifier order has seemingly switched.