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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> |
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| <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. |
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| [[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.