- #1
rukawakaede
- 59
- 0
Suppose set [tex]A=\{\{\omega\}:\omega\in\mathbb{R}\}[/tex]. What can you say more about it? In particular, on the [tex]\sigma(A)[/tex] the smallest sigma field generated by [tex]A[/tex], i.e. it is closed under complements/countable intersections or unions and the whole space is in the sigma field.
Clearly, if here [tex]\mathbb{R}[/tex] replace to a finite space [tex]\Omega[/tex], then [tex]\sigma(\Omega)=\mathcal{P}(\Omega)[/tex] since all subset of [tex]\Omega[/tex] can be written as a countable union of singletons of [tex]\Omega[/tex].
But it is not true for space which is uncountably infinite like [tex]\mathbb{R}[/tex].
My initial thought is that [tex]\sigma(A)[/tex] does not contain intervals in [tex]\mathbb{R}[/tex]. However i am not sure if I miss anything?
Clearly, if here [tex]\mathbb{R}[/tex] replace to a finite space [tex]\Omega[/tex], then [tex]\sigma(\Omega)=\mathcal{P}(\Omega)[/tex] since all subset of [tex]\Omega[/tex] can be written as a countable union of singletons of [tex]\Omega[/tex].
But it is not true for space which is uncountably infinite like [tex]\mathbb{R}[/tex].
My initial thought is that [tex]\sigma(A)[/tex] does not contain intervals in [tex]\mathbb{R}[/tex]. However i am not sure if I miss anything?