**Reference: Introductory Real Analysis, Kolomogorov and Fomin, Dover Publications, Translated and edited by Richard A. Silverman:**

Problem 1:

Let X be an uncountable set, and be the ring consisting of all finite subsets of X and their complements. Is a -ring also?

Problem 2:

Are open intervals Borel sets ?

Problem 3:

Let be a function defined on a set M and taking values in a set N. Let be a system of subsets of M, and let denote the system of all images of sets . Moreover, let be a system of subsets of N, and let denote the system of all preimages of of sets . Prove that

(i) If is a ring, so is

(ii) If is an algebra, so is

(iii) If is a borel algebra, then so is

(iv)

(v) .

Which of these assertions remain true if os replaced by and by f?

Regards,

Nalin Pithwa

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