15. If S1 and S2 are two semialgebras of subsets of S, show that the class S1S2 := {A1A2 : A1 e S1, A2 e S2} is again a semialgebra of subsets of N. The field (o-field) generated by S1S2 is identical...

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Extracted text: 15. If S1 and S2 are two semialgebras of subsets of S, show that the class S1S2 := {A1A2 : A1 e S1, A2 e S2} is again a semialgebra of subsets of N. The field (o-field) generated by S1S2 is identical with that generated by Si U S2.