In mathematics, a nonempty collection of sets
-
A ∪ B ∈ R ifA , B ∈ R -
A − B ∈ R ifA , B ∈ R -
⋂ n = 1 ∞ A n ∈ R ifA n ∈ R for alln ∈ N
If only the first two properties are satisfied, then
δ-rings can be used instead of σ-fields in the development of measure theory if one does not wish to allow sets of infinite measure.
References
Delta-ring Wikipedia(Text) CC BY-SA