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.