Could you remind what B(R)*B(R) is?
I've a quick question about Borel algebra. The Borel algebra on set X is defined as the smallest σ-algebra containing all open sets (or, equivalently, all closed sets). Let R be the set of reals and B(R) denote the Borel algebra on R. Then my question is: whether B(R)*B(R) equals B(R2)? How do you prove or disprove this?