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## Main Question or Discussion Point

Can someone help me with this question ?

Let

(a) Let

(b) Show that

Let

*F*and*G*be σ-fields os subsets of*S*.(a) Let

*H*=*F*intersection*G*be the collection of subsets of*S*lying in both*F*and*G*. Show that*H*is a σ-field.(b) Show that

*F*union*G*, the collection of subsets of*S*lying in either*F*or*G*, is not necessarilt a σ-field.