Infinitely often and almost always

From Machinelearning
Revision as of 21:43, 31 July 2019 by IssaRice (talk | contribs)

Let A1,A2,A3,… be a sequence of events in some sample space Ω.

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 ω∈⋂N=1∞⋃n=N∞An ω∈⋃N=1∞⋂n=N∞An
first-order quantifiers ∀N≥1∃n≥N:ω∈An ∃N≤1∀n≥N:ω∈An
verbal expression ω∈An for infinitely many n≥1 ω∈An for almost all n≥1, i.e. ω∈An for all but finitely many n≥1, i.e. ω∉An for finitely many n≥1
lim sup/lim inf ω∈lim supn→∞An ω∈lim infn→∞An
limit of sup/inf ω∈limN→∞⋃n=N∞An ω∈limN→∞⋂n=N∞An